Terra Invicta Official Wiki - User contributions [en]

Terrestrial Warfare

2026-03-29T10:11:56Z

76561197989421583: /* 1. Hit Chance (The Accuracy Gap) */

This page mainly discusses the mechanics for fighting terrestrial wars. For a more detailed discussion about starting and ending wars, see [[Foreign Relations#Wars]] instead.

[[Foreign Relations#Wars|Wars]] begin when a [[Councilors|councilor]] for the executive [[Factions|faction]] of one of two [[Foreign Relations#Rivals|Rivals]] selects the [[Foreign Relations#Declaring_Wars|War policy]] against the rival. All war-capable [[Foreign Relations#Alliances|allies]] of the defending rival (with an army or nuclear weapons) join the war. All war-capable allies of the attacker are given the option to join on the attacker's side.

To win a war, an [[Nations#Armies|army]] must occupy the enemy's {{icon|capital|bgcolor=DarkSlateGray}}Capital [[Regions|region]]. At that moment, the war ends, triggering a [[Foreign Relations#War_Conquest|regime change]]. [[Foreign Relations#Claims|Claimed regions]] change hands to the occupier and its allies. If any of the invaded nation remains, its control point owners are replaced with those of the victor. Some of the nation's stats change when a new regime is installed, sometimes in unpredictable ways, but the new ruling faction will be able to fund [[Nations#Direct_Investment|Direct Investments]] into the nation at greatly reduced {{TV|influence}} cost for a period of one year. Unoccupied [[Regions]] and surviving enemy armies will contribute to greater {{TV|unrest}} following a regime change.

Wars may also end with a [[Foreign Relations#Seeking_Peace|simple peace]] where both sides return to the prewar status quo.

== Armies ==

[[Nations#Armies|Armies]] represent multiple modern divisions that are capable of gaining and holding territory in other [[Nations]]. Control of an army is gained after councilors gain at least partial control of a nation. Most [[Nations]] don't have armies at the campaign start, but [[Nations]] with sufficient {{TV|pop}} can build new ones with enough investment into the {{TV|build army}}. While powerful, armies are a drag on a nation's {{icon|ip|bgcolor=DarkSlateGray}}economic development and remain subject to the international relations of their home countries, which too can be managed with sufficient control of a nation.

Armies have a [[File:ICO army HQ.png|20px]]headquarters region in their home nation. If located there, they incur a smaller cost to the nation's {{icon|ip|bgcolor=DarkSlateGray}}economic development.

Armies rely on two key values: its parent nation's {{TV|miltech}} level and its strength. The strength value measures how much damage the army has taken. Armies usually passively and freely repair themselves when not fighting in a friendly region.

Some armies have a {{icon|navy}}[[Nations#Navies|Navy]] upgrade that allows them to transit oceans. During wartime, a nation's navies can only cross the water if the nation has naval superiority over its foes. Only larger or wealthier [[Nations]] have the capability to {{icon|build navy}}build and project power with {{icon|navy}}navies.

=== Naval Freedom ===

For each [[Foreign Relations#Wars|war]], the game computes for each side the sum of the {{TV|miltech}} of the armies that have a navy upgrade. If one side has a higher sum than the other, then the other side of the war is blockaded: all of its nations no longer have Naval Freedom.

As a result, a nation only has Naval Freedom if it is not blockaded in any of the wars that it is involved in.

Notably, since wars can get very messy, with multiple overlapping wars, it is actually entirely possible for all nations to lose their Naval Freedom.

Consider a simple example with 3 nations: A, B, and C, such that:
* A has a single navy with {{TV|miltech|3}}.
* B has a single navy with {{TV|miltech|2}}.
* C has a single navy with {{TV|miltech|2}}.

Suppose there are three overlapping wars X, Y, and Z, such that:
* War X pits A against B.
* War Y pits A against C.
* War Z pits A against B and C.

Then the result would be:
* War X blockades B, since A's 3 naval score beats B's 2 naval score.
* War Y blockades C, since A's 3 naval score beats C's 2 naval score.
* War Z blockades A, since A's 3 naval score is beaten by the combined naval score of B's 2 naval score added to C's 2 naval score = 4 naval score.

So all 3 nations have no Naval Freedom.

=== Army Movement ===

Armies are allowed to be in any region R such that one of the following is true:
* R belongs to the army's home nation.
* R belongs to a nation that is [[Foreign Relations#Alliances|allied]] to the army's home nation.
* R belongs to a nation that is [[Foreign Relations#Wars|at war]] with the army's home nation.

An army can directly travel from any region R1 to any region R2 such that at least one of the following is true:
* R1 and R2 are adjacent.<ref name=adjacent>Note: Certain research projects can make pairs of regions become adjacent.</ref>
* R1 and R2 are adjacent only for friendly armies<ref name=adjacent />, and both R1 and R2 belong to nation(s) that are not at war with the army's home nation.
* All of the following are true:
** R1 and R2 both currently have [[Regions#World_Ocean_Access|world ocean access]].
** The army's home nation has [[Terrestrial_Warfare#Naval_Freedom|naval freedom]].
** Either the army does not need to travel between the Black Sea and the World Ocean, or the army's home nation has access to the Turkish Strait.

A nation has Turkish Strait access as long as one of the following is true:
* It is not at war with the nation that owns the Istanbul region.
* The Istanbul region is fully occupied.

<references />

==== Land Movement ====

The time needed for an army to travel directly between two adjacent regions without using a navy is calculated as follows:
<pre> Duration (days) = Distance (km) / 300 (km/day) * 4 / Miltech </pre>

But this value is affected by the following multipliers:
{| class="wikitable sortable" style="text-align:center;"
|-
! rowspan=2| Condition(s) !! colspan=3|Multiplier Value When:
|-
! Only Origin Region is Small<ref name=small>A region is small if it is smaller than 150000km².</ref> !! Only Destination Region is Small<ref name=small />!! Otherwise
|-
| Origin Region is not friendly OR Origin Region has enemy armies || 5 ^ 0.2 || 5 ^ 0.8 || 5 ^ 0.5
|-
| (Origin Region is not friendly OR Origin Region has enemy armies) AND Origin Region is {{icon|rugged}}Rugged || 1.5 ^ 0.2 || 1.5 ^ 0.8 || 1.5 ^ 0.5
|-
| Origin Region is friendly AND Origin Region has no enemy armies AND Origin Region is {{icon|rugged}}Rugged || 1.25 ^ 0.2 || 1.25 ^ 0.8 || 1.25 ^ 0.5
|-
| Origin Region is friendly AND Origin Region has no enemy armies AND Origin Nation has {{TV|unrest|>5}} || (1 + (Origin Nation {{TV|unrest}} - 5) / 6.5) ^ 0.2 || (1 + (Origin Nation {{TV|unrest}} - 5) / 6.5) ^ 0.8 || (1 + (Origin Nation {{TV|unrest}} - 5) / 6.5) ^ 0.5
|-
| Origin Region is a {{icon|colony|bgcolor=DarkSlateGray}}Colony || 1.5 ^ 0.2 || 1.5 ^ 0.8 || 1.5 ^ 0.5
|-
| Destination Region is not friendly || 5 ^ 0.8 || 5 ^ 0.2 || 5 ^ 0.5
|-
| Destination Region is not friendly AND Destination Region is {{icon|rugged}}Rugged || 1.5 ^ 0.8 || 1.5 ^ 0.2 || 1.5 ^ 0.5
|-
| Destination Region is friendly AND Destination Region is {{icon|rugged}}Rugged || 1.25 ^ 0.8 || 1.25 ^ 0.2 || 1.25 ^ 0.5
|-
| Destination Region is friendly AND Destination Nation has {{TV|unrest|>5}} || (1 + (Destination Nation {{TV|unrest}} - 5) / 6.5) ^ 0.8 || (1 + (Destination Nation {{TV|unrest}} - 5) / 6.5) ^ 0.2 || (1 + (Destination Nation {{TV|unrest}} - 5) / 6.5) ^ 0.5
|-
| Destination Region is a {{icon|colony|bgcolor=DarkSlateGray}}Colony || 1.5 ^ 0.8 || 1.5 ^ 0.2 || 1.5 ^ 0.5
|}

<references />

==== Naval Movement ====

The time needed for an army to travel between two regions without using a navy is calculated as follows:
<pre> Duration (days) = (14 days + Distance (km) / 792 (km/day) ) * 4 / Miltech </pre>

But this value is affected by a number of complex calculations that consider the different possible sea routes. In particular, the duration can be significantly affected by whether the army's nation has access to the Suez and Panama canals.

A nation has canal access as long as one of the following is true:
* It is not at war with the nation that owns the Canal region.
* The Canal region is fully occupied.

The Canal regions are:
* Cairo for the Suez Canal.
* Panama City for the Panama Canal.

=== Army Battle ===

==== Simplified Combat Rules ====

Combat in ''Terra Invicta'' is a comparison of Miltech levels. Higher Miltech means you hit more often and deal more damage. If two forces have equal Miltech, the base hit chance is 50%.

===== 1. Hit Chance (The Accuracy Gap) =====
The game calculates the difference (Δ) between the Attacker's Miltech and the Defender's Miltech.

If Miltechs are equal: 50% Hit Chance.
If you have the advantage: Your hit chance climbs toward 100%.
If you are outclassed: Your hit chance drops toward 0%.

Hit Chance (Advantage)=100%−(50%×0.775)^(1.5×Δ)
Hit Chance (Disadvantage)=50%×0.775^(1.5×Δ)

====== Hit Chance Reference Table ======

The following table shows the 1vs1 hit chance based on the Miltech difference (Delta = Attacker Miltech - Defender Miltech).

{| class="wikitable" style="text-align: center;"
|-
! Miltech Difference (Delta) !! Hit Chance !! Note
|-
| '''+3.0''' || '''84.1%''' ||
|-
| '''+2.0''' || '''76.7%''' ||
|-
| '''+1.0''' || '''65.9%''' || '''Strong offensive edge.'''
|-
| +0.8 || 63.2% ||
|-
| +0.6 || 60.3% ||
|-
| +0.4 || 57.1% ||
|-
| +0.2 || 53.7% ||
|-
| '''0.0''' || '''50.0%''' || '''Even match; coin-flip odds.'''
|-
| -0.2 || 46.3% ||
|-
| -0.4 || 42.9% ||
|-
| -0.6 || 39.7% ||
|-
| -0.8 || 36.8% ||
|-
| '''-1.0''' || '''34.1%''' || '''Struggling to land hits.'''
|-
| '''-2.0''' || '''23.3%''' ||
|-
| '''-3.0''' || '''15.9%''' ||
|}

===== 2. Damage Formulas =====
Damage is calculated as a percentage of the defender’s Max Health.

====== Army vs. Army ======
When an army hits another army, it '''deals roughly 10% of its Miltech in percentage of defender’s Max Health'''.

Base Damage: Miltech × 0.1 (±20%)

Variance: ±20% is the game simulating a damage range mechanic.

Critical Hit: Usually 1x. Increases to 3x if the attacker is at full health and the region is unoccupied (an "Ambush"), or by a small random chance based on the total number of armies in the fight.

====== Region vs. Army ======
Region defenses (fortifications/militia) '''fire every day at every hostile army'''. They deal less base damage but have much higher "Critical" lethality.

Base Damage: Region Miltech × 0.0225

The "Lethality" Multiplier: If an army is at full health and the region is unoccupied, the region can deal a massive 100x damage critical hit.

Overwhelmed Defenses: If more hostile armies are present than friendly armies, the region's damage output is reduced.

====== Occupying a Region (Army vs. Region) ======
When an army hits region defenses, it increases the Occupation %.

Base Damage: Army Miltech × 0.0225

Advantage Bonus: If your Army Miltech is higher than the region's base tech, you gain occupation faster.

Geography Modifiers: Occupation is slower in regions with huge populations (like Delhi) or massive land areas (like Siberia).

Crowding Penalty: Having too many armies in one spot (more than 1 per 100,000 km2) slows down occupation by up to 50%.

==== Combat Rules ====

Combat occurs whenever an army A is in a [[Regions|region]] R such that at least one of the following is true:
* A's home nation is [[Foreign_Relations#Wars|at war]] with the home nation of another army in R.
* R is partially or fully occupied and A's home nation owns R.
* R is partially or fully occupied and A's home nation is [[Foreign_Relations#Alliances|allies]] with the nation that owns R.
* A's home nation is [[Foreign_Relations#Wars|at war]] with the nation that owns R and R is not fully occupied.
* A's home nation does not exist and R is not fully occupied.
{{SpoilerBox|Alien-Related}}
* There is a [[Aliens#Megafauna|Megafauna Army]] in R that is not owned by the same faction that owns A.
* A's home nation is [[Foreign_Relations#Wars|at war]] with the nation that owns R and A is an [[Aliens#Invader_Armies|Invader Army]] and R is fully occupied by a war alliance that does not include the [[Aliens#Alien_Administration|Alien Nation]].
* A's home nation does not exist and A is an [[Aliens#Invader_Armies|Invader Army]] and R is fully occupied by a war alliance that does not include the [[Aliens#Alien_Administration|Alien Nation]].
* A is a [[Aliens#Megafauna|Megafauna Army]] that is owned by the {{icon|alien}}[[Aliens]] and R is not part of the [[Aliens#Alien_Administration|Alien Nation]] and R is not owned by a nation whose executive is controlled by a faction that has researched [[Xenofauna Harmony]].
* A is a [[Aliens#Megafauna|Megafauna Army]] that is owned by a faction F that is '''not''' the {{icon|alien}}[[Aliens]] and every non-[[Aliens#Megafauna|Megafauna]] army in R that is owned by F is owned by a nation that is [[Foreign_Relations#Wars|at war]] with the nation that owns R.
{{SpoilerBoxEnd}}

Combat is simulated as a daily exchange of attacks. For each army A:
# If there is an enemy army in the combat region, then A randomly selects one to fire at, preferring to avoid any armies owned by the same faction as A.
# If A is within a region that is hostile to A, then the region defenses fires at A.
# If A did not fire at anyone in the first step AND the region defenses missed its attack on A, then A fires at the region defenses.

Note that this means every army can fire at most one attack per day, but region defenses fire an attack on every hostile army every day.

Every attack has a hit chance that is determined by the gap between the attacker's {{TV|miltech}} and the defender's {{TV|miltech}}. But several modifiers may be applied to each side's {{TV|miltech}}, including but not limited to {{MissionIcon|Advise}}[[Advise|Advising]] [[Councilors]], {{icon|rugged}}rugged terrain bonuses, and damage taken.

When attacks hit, damage is taken, which scales based on the attacker's {{TV|miltech}}. When armies take damage, their health % drops. When region defenses take damage, their occupation % increases.

If a region is fully occupied it ceases fighting, but it can't change hands until the war is concluded. Regional economies and space facilities can take significant [[Regions#Region_Damage|collateral damage]] during fighting, although the rate of damage goes down as {{{TV|miltech}} goes up (representing more precise weaponry). Sufficient collateral damage will count as an [[Factions#Atrocity|atrocity]] by the army's owning faction.

==== Formulas ====

'''Miltech Calculations:'''

{| class="wikitable"
|-
! Factor !! Army Miltech A !! Army Miltech B !! Region Miltech
|-
| Base Miltech || Base Miltech || Base Miltech || Base Miltech
|-
| Councilor {{MissionIcon|Advise}}[[Advise]] Bonus || +0.01 per {{TVS|command}} || +0.01 per {{TVS|command}} || +0.01 per {{TVS|command}}
|-
| LEO Hab Bonus (capped at +0.3) || +0.03 per Military Lab || +0.03 per Military Lab || No Effect
|-
| In Home Nation || +0.2 || +0.2 || No Effect
|-
| In Home Nation AND region is {{icon|rugged}}rugged || +0.2 || +0.2 || +0.2
|-
| In Home Nation AND region is {{icon|core economic region|bgcolor=DarkSlateGray}}core economic || +0.1 || +0.1 || +0.1
|-
| Region is {{icon|rugged}}rugged and [[Mountain Warfare Doctrine]] is researched || +0.125 || +0.125 || +0.125
|-
| Region is {{icon|core economic region|bgcolor=DarkSlateGray}}core economic and [[Urban Warfare Doctrine]] is researched || +0.125 || +0.125 || +0.125
|-
| Army CP is disabled (Abandoned or {{MissionIcon|Crackdown}}[[Crackdown]]ed) || -0.2 || -0.2 || No Effect
|-
| In Allied (or Home) Nation || +0.05 per {{TV|cohesion}} of Allied Nation || No Effect || No Effect
|-
| Home Nation's {{TV|cohesion}} || No Effect || No Effect || +0.05 per {{TV|cohesion}}
|-
| Home Nation's {{TV|unrest}} || No Effect || No Effect || -0.05 per {{TV|unrest}}
|-
| Adjacent Regions belonging to Same Home Nation || No Effect || No Effect || +Fraction of such Regions that are unoccupied and not fighting × Home Nation's Miltech × 0.1 × (1 - 0.05 × Home Nation's {{TV|unrest}})
|-
| Remaining Combat Effectiveness || × (1 - 0.5 × Lost Health %) || × (1 - 0.5 × Lost Health %) || × (1 - 1/3 × Occupation %)
|-
|}

Note: If a nation has not completed the {{TV|found military}}, then its regions have effectively {{TV|miltech|0}} for combat.

'''Hit Chance Calculation:'''
* When an army fires at another army, the attacking army uses its '''Army Miltech A''' as the Attack value, while the defending army uses its '''Army Miltech B''' as the Defense value.
* When region defenses fire at an army, the region defenses use '''Region Miltech''' as the Attack value, while the defending army uses its '''Army Miltech A''' as the Defense value.
* When an army fires at the region defenses, the hit chance is always '''100%'''. (But the army only fires if the region defenses missed their attack.)

{| class="wikitable"
|-
! Condition
! Formula
|-
| Defense ≥ Attack
| <code>50% × 0.775^(1.5 × (Defense-Attack))</code>
|-
| Attack > Defense
| <code>100% − (50% × 0.775^(1.5 × (Attack-Defense)))</code>
|}

'''Damage taken:'''
When an army successfully lands a hit on another army, the defending army loses X% of its max health, where X calculated as follows:
# Set X to the attacking army's '''Army Miltech A'''.
# Multiply X by 0.1.
# Multiply X by a random value between 0.8 and 1.2.
# Multiply X by a critical multiplier Z, calculated as follows:
## Set Z to 1.
## Y% chance to set Z to 3, where Y is the square of the number of armies in the region that are involved in the war (allied armies that aren't part of the war don't count).
## If the attacking army is at full health and neither army is a [[Aliens#Megafauna|Megafauna]] and the region is 0% occupied, set Z to 3.
# All army damage bonuses from [[Technology|Projects]] are applied to X. (These bonuses are multiplicative and compounding, but often require the defending army to be a specific type of army.)

When the region defenses successfully land a hit on an army, the defending army loses X% of its max health, where X calculated as follows:
# Set X to the region's '''Region Miltech'''.
# Multiply X by 0.0225.
# Multiply X by a random value between 0.8 and 1.2.
# Let Y be the number of region-friendly armies in the region that are involved in the war (allied armies that aren't part of the war don't count) multiplied by the square of the number of region-hostile armies in the region.
# Multiply X by a critical multiplier Z, calculated as follows:
## Set Z to 1.
## Y% chance to set Z to 40.
## If the region is 0% occupied and the defending army is at full health, then set Z to 100.
## If Z is not 100, another Y% chance to set Z to 40.
## If Z is less than 40, (Y% / (100% - Y%)) chance to set Z to 5.
# All army damage bonuses from [[Technology|Projects]] are applied to X, except for bonuses against [[Aliens#Megafauna|Megafauna]]. (These bonuses are multiplicative and compounding, but often require the defending army to be a specific type of army.)
# Let H be the sum of the Remaining Combat Effectiveness multipliers of every region-hostile army in the region.
# Let F be the sum of the Remaining Combat Effectiveness multipliers of every region-friendly army in the region that is involved in the war (allied armies that aren't part of the war don't count).
# If H - F is more than 0, then multiply X by 1 - (H - F) / (H - F + 2).
# (1 - Region occupation % by defending army's home nation / H) chance to multiply X by 2.

If this last (1 - Region occupation % by defending army's home nation / H) chance fails, the region occupation % by the defending army's home nation actually '''decreases''' by D%, where D is calculated as follows:
# Set D to the region's Region Miltech.
# Multiply D by 0.0225.
# Multiply D by a random value between 0.8 and 1.2.
# Divide D by the number of region-hostile armies in the region.
# Multiply D by the '''Region Combat Action Multiplier''', which is calculated as 2 / (Region Population ^ 0.75 / Game Start Mean Average Region Population ^ 0.75 + Region Area ^ 0.5 / Median Region Area ^ 0.5).
# If D > 10, then set D to 10.

When an army hits the region defenses, the attacking army's home nation increases its occupation % of the region by X%, where X is calculated as follows:
# Set X to the attacking army's '''Army Miltech A'''.
# Let G be X - the defending region's home nation's base {{TV|miltech}} - the Councilor {{MissionIcon|Advise}}[[Advise]] Bonus for the defending region's home nation.
# If G > 0 then add G to X.
# Multiply X by 0.0225.
# Multiply X by a random value between 0.8 and 1.2.
# Multiply X by the '''Region Combat Action Multiplier''', which is calculated as 2 / (Region Population ^ 0.75 / Game Start Mean Average Region Population ^ 0.75 + Region Area ^ 0.5 / Median Region Area ^ 0.5).
# Multiply X by a critical multiplier Z, calculated as follows:
## Set Z to 1.
## Y% chance to set Z to 40.
## If the region is 0% occupied and the defending army is at full health, then set Z to 100.
## If Z is not 100, another Y% chance to set Z to 40.
## If Z is less than 40, (Y% / (100% - Y%)) chance to set Z to 5.
# Let C be the number of region-hostile armies in the region - the region area / 100000km².
# If C > 0, then multiply X by Max(1 - C * 0.02, 0.5)
# If X > 10, then set X to 10.

=== Army Operations ===
The faction that controls an army can conduct operations with it. They are:
{| class="wikitable"
! Operation !! width=85% | Effects
|-
| [[File:ICO DeployArmyOperation on.png|40px]] Deploy Army
| Move this Army to an adjacent region, including those of allies or wartime enemies. Armies will engage in battle with enemy armies and occupy enemy regions.
|-
| [[File:ICO DeployArmiesOperation on.png|40px]] Deploy Armies
| Move all stacked armies to an adjacent region, including those of allies or wartime enemies. Armies will engage in battle with enemy armies and occupy enemy regions.
|-
| [[File:ICO AssaultAlienAssetOperation on.png|40px]] Assault Alien Asset
| Launch an assault on a fixed alien target.
|-
| [[File:ICO AssaultSpaceFacilityOperation on.png|40px]] Assault Space Facility
| Destroy a fixed space facility in the region.
|-
| [[File:ICO RazeRegionOperation on.png|40px]] Raze Region
| Launch a general attack on economic and civilian targets in this region. Commits 5 to 25 [[Factions#Atrocity|atrocities]].
|-
| [[File:ICO ArmyGoHomeOperation on.png|40px]] Airlift Home
| Return this army to its home region during peacetime. Operation will not complete if home nation is at war.
|-
| [[File:ICO CancelArmyOperation on.png|40px]] Cancel Operation
| Cancel current operation for this Army. Army will resume fighting if enemies are present.
|}

'''Wiki Help wanted''': Look up the in-game image and description for the Army Annex Region operation and upload both here!

==== Annex Region ====

The game mechanics for army annex operations are explained here [[Foreign Relations#War_Annexation]].

==== Raze Region ====

See [[Regions#Region_Damage]].

==== Assault Alien Asset ====

{| class="wikitable"
|+ Damage Taken by {{TV|armies}} when they Assault Alien Assets
|-
! rowspan=2 | Mission Outcome !! colspan=2 | Type of Alien Asset
|-
! [[Aliens#Alien_Xenoforming|Xenoflora]] !! Other
|-
| Critical Failure || (30% to 150%) / Base {{TV|miltech}} || (150% to 300%) / Base {{TV|miltech}}
|-
| Normal Failure || (15% to 112.5%) / Base {{TV|miltech}} || (75% to 225%) / Base {{TV|miltech}}
|-
| Normal Success || (0% to 75%) / Base {{TV|miltech}} || (0% to 150%) / Base {{TV|miltech}}
|-
| Critical Success || (0% to 15%) / Base {{TV|miltech}} || (0% to 30%) / Base {{TV|miltech}}
|}

Note: Base {{TV|miltech}} is simply the army's home nation's {{TV|miltech}}, with all modifiers ignored.

See [[Aliens]] for spoilers on the different types of alien assets that can be assaulted, as well as the consequences of such assaults.

=== Army Healing ===

An injured human army will passively heal over time when all of the following conditions are true:
* It is in a friendly region<ref>A region owned by its home nation or a nation allied to its home nation</ref>.
* The region is currently not occupied or being occupied.
* It is not in battle with other armies.
* It is not currently performing an operation.

The % health that gets healed each day is calculated as follows:
# 0.5% Base.
# +0.5% more if the faction that controls the army also controls the [[Nations#Control_Point_Types|Defense Sector Control Point]] of the army's home nation.
# +0.5% more if the army is in its home nation.
# +0.5% more if the army is in its home region.
# Multiply the total by (1 - (Currently Healing Human Armies of Home Nation / (Total Human Armies of Home Nation + 1))).
#* Note: This step is currently bugged to never occur.
# +0.5% more if the faction that controls the army has researched the [[Rapid Repairing Materials]] project.
# +0.5% more if the faction that controls the army has researched the [[Predictive Logistics Systems]] project.

{{SpoilerBox|Alien-Related}}
Human armies that are owned by the {{icon|alien}}[[Aliens]] still follow the same healing rules.

But for the healing mechanics of Alien-related armies, see [[Aliens#Megafauna]] and [[Aliens#Invader_Armies]] instead.
{{SpoilerBoxEnd}}

<references />

=== Army Death ===

Whenever an army dies, multiple effects may occur:

==== Democracy Penalties ====

If the dead army belonged to a democratic human nation, then that nation suffers two penalties:
* A {{TV|cohesion}} loss equal to the nation's {{TV|democracy}} / 10.
* Applies [[Nations#Changing_Public_Opinion|Propaganda]] in the nation for the faction that owned the dead army. Propaganda strength is equal to (0 - the nation's {{TV|democracy}}).

==== Army IP Refund ====

Whenever a human army dies, its home [[Nations|nation]] receives a fraction of its {{TV|IP}} Cost as a refund. This refund is put directly into the {{TV|build army}} and/or {{TV|build navy}}, so it can often result in new {{TV|armies}} and/or {{TV|navies}} being built the next day. Specifically, the refund amounts are calculated as follows:

{| class="wikitable sortable" style="text-align:center;"
|+ Refund Amounts for {{TV|build army}}. Only applies if army did not die by nuke.
|-
! Army Died in Home Nation? !! Refund Amount
|-
| Yes || (30% to 50%) of {{TV|build army}} cost.
|-
| No || (15% to 25%) of {{TV|build army}} cost.
|}

{| class="wikitable sortable" style="text-align:center;"
|+ Refund Amounts for {{TV|build navy}}. Only applies if the dead army had a navy.
|-
! Army Died in Home Nation? !! Home Nation has [[Terrestrial_Warfare#Naval_Freedom|Naval Freedom]]? !! Army Died in Region that currently has [[Regions#World_Ocean_Access|World Ocean Access]]? !! Refund Amount
|-
| Yes || Yes || Yes || (70% to 90%) of {{TV|build navy}} cost.
|-
| Yes || Yes || No || (90% to 110%) of {{TV|build navy}} cost.
|-
| Yes || No || || (20% to 30%) of {{TV|build navy}} cost.
|-
| No || Yes || Yes || (60% to 80%) of {{TV|build navy}} cost.
|-
| No || Yes || No || (80% to 100%) of {{TV|build navy}} cost.
|-
| No || No || || (10% to 20%) of {{TV|build navy}} cost.
|}

==== Complete Milestones ====

If the army is related to the [[Aliens]] in any way, then the faction that kills it may achieve certain milestones from doing so. See [[Aliens]] for details.

==== Hate Vent ====

See [[Diplomacy#Alien_Hate_Vent]].

== Nuclear Warfare ==
Some nations have a number of {{TV|nukes}} available to them. These represent launching multiple strategic nuclear weapons at a target region. Launching nuclear strikes will devastate the economy of a [[Regions|region]] and the enemy {{TV|armies}} within it, although the damage will be somewhat mitigated if a nation is launching strikes on its own or an [[Foreign_Relations#Alliances|ally]]'s territory. Launching factions will be charged with committing one or more [[Factions#Atrocity|atrocities]]. Detonating a sufficient number of nuclear weapons may also have disastrous global effects. A region with {{icon|sto defense}}space defenses cannot be attacked with {{TV|nuke}}.

Nations can develop nuclear weapon with the {{TV|develop atomic bomb}}, which also gives {{TV|nuke|1}}. A nation with nuclear weapon program can build more with the {{TV|nuclear weapons}}.

Nations construct nuclear weapons as a deterrent to enemy invasion. Attempting to conquer a nuclear-armed nation will almost certainly lead to nuclear strikes in retaliation.

=== Valid Targets for a Nuclear Strike ===

Nukes can only be fired at [[Regions]]. The set of regions that a [[Nations|nation]] X can fire a nuke at is computed as follows:
# Add every region that is owned by any nation that is [[Foreign_Relations#Wars|at war]] with X.
# If X does not have a spaceflight program, then remove every region that is not adjacent to X and does not have [[Regions#World_Ocean_Access|ocean access]].
# If X does not have a spaceflight program and does not have [[Terrestrial_Warfare#Naval_Freedom|naval freedom]], then remove every region that is not adjacent to X.
# Add every region owned by X or an [[Foreign_Relations#Alliances|ally]] of X if the region currently contains an army that is owned by any nation that is [[Foreign_Relations#Wars|at war]] with X.
# For every region R, remove R unless one of the following is true:
#* R is owned by X.
#* R is owned by an [[Foreign_Relations#Alliances|ally]] of X.
#* R is owned by a nation that is [[Foreign_Relations#Wars|at war]] with X and R does not have a [[Nations#Space_Defenses|space defense facility]] built.

=== Effects of a Nuclear Strike ===

Launching nuclear weapons will do terrible and lasting damage to the targeted region, destroy any enemy {{TV|armies}} and all space facilities, and surely be seen with horror around the globe.

{| class="wikitable"
|+ Effects of a Nuclear Attack (In Chronological Order)
|-
! Category !! Amount for Offensive Nukes !! Amount for Defensive Nukes !! Modifiers
|-
| Target [[Nations#GDP_Per_Region|Region GDP]] || -52.5% to -87.5% || -15% to -25%
| rowspan=2 |
* [[Urban Armoring]] multiplies amount by 0.8.
* [[Civil Defense Programs]] multiplies amount by 0.8.
|-
| Target {{icon|pop}}[[Nations#Population|Region Population]] || -18.75% to -31.25% || -1.875% to -3.125%
|-
| Target Nation [[Nations#Sustainability|Pollution Multiplier]] || +0.075 to +0.125 || +0.00375 to +0.00625 || Multiplied by [[Nations#GDP_Per_Region|Region GDP]] / [[Nations#GDP|Nation GDP]]
|-
| Nuking Faction Commits [[Factions#Atrocity|Atrocities]] || colspan=2 | 1 per 100k {{TV|pop}} killed (rounded down).
|
* Multiply by 10 if nuke launcher is not on the defending side of any war where the target nation is on the attacking side.
** ...seems to apply for self-nukes too??
{{SpoilerBox|Alien-Related}}
** Does not apply if the target region is owned by the [[Aliens#Alien_Administration|Alien Nation]].
{{SpoilerBoxEnd}}
* Capped between 1 and 20.
|-
| All Human Nations' GDP || -25% × [[Nations#GDP_Per_Region|Region GDP]] / Global GDP + (0% to -2%) || -5% × [[Nations#GDP_Per_Region|Region GDP]] / Global GDP + (0% to -2%) || None
|-
| [[Family Ties]] Trait Effect || colspan=2 | {{TV|loyalty|-10}} || Multiply by 2 if Councilor's Faction launched the nuke.
|-
| Target Region is {{icon|core economic region|bgcolor=DarkSlateGray}}Core Economic || Remove {{icon|core economic region|bgcolor=DarkSlateGray}}Core Economic status || Nothing || None
|-
| All Human Nations' [[Nations#GDP|GDP]] || -2.5% + (0% to -2%) || N/A || If Target Region just lost {{icon|core economic region|bgcolor=DarkSlateGray}}Core Economic status.
|-
| Target Region is {{icon|oil region}}Core Oil or {{icon|resource region}}Core Mining || Remove {{icon|oil region}}Core Oil or {{icon|resource region}}Core Mining status || Nothing || None
|-
| All Human Nations' [[Nations#GDP|GDP]] || -1.5% + (0% to -2%) || N/A || If Target Region just lost {{icon|oil region}}Core Oil or {{icon|resource region}}Core Mining status.
|-
| Target Nation [[Nations#Priorities|Priorities]] || colspan=2| Set to 0 || Except {{icon|spoils}}Spoils, {{icon|unity}}Unity, and {{icon|oppression}}Oppression.
|-
| rowspan=2 | Destroy Space Assets in Target Region || colspan=2 | All {{icon|boost}}[[Nations#Boost|Boost]], {{icon|mc}}[[Nations#Mission_Control|Mission Control]] , and {{icon|sto defense|bgcolor=DarkSlateGray}}[[Nations#Space_Defenses|Space Defenses]] || If Target Nation is NOT Nuke Launcher
|-
| N/A || All {{icon|boost}}[[Nations#Boost|Boost]] and {{icon|sto defense|bgcolor=DarkSlateGray}}[[Nations#Space_Defenses|Space Defenses]], just 1 {{icon|mc}}[[Nations#Mission_Control|Mission Control]] || If Target Nation is Nuke Launcher
|-
| Target Nation {{icon|funding}}[[Nations#Funding|Funding]] || N/A || -50% × [[Nations#GDP_Per_Region|Region GDP]] / [[Nations#GDP|Nation GDP]] || If Target Nation is Nuke Launcher
|-
| rowspan=7 | Health of Each Army in Target Region || colspan=2 | Instant Death || For the Strongest<ref>The strongest army is the army whose health % × Base {{TV|miltech}} is the highest.</ref> Army that is not Ally of Nuker<ref name=allyofnuker>An army is an ally of the nuker if any of the following are true:
* The army is owned by the nuking nation.
* The army is owned by an ally of the nuking nation.
* The army is owned by the nuking faction and not a [[Aliens#Megafauna|Megafauna]].</ref>.
|-
| colspan=2 | Min(0%, (-100% + (1% to 5%) × (Base {{icon|miltech}}MilTech - 3.79)) × 0.140625) || For each [[Aliens#Invader Armies|Alien Invader Army]] that is not Ally of Nuker<ref name=allyofnuker />.
|-
| colspan=2 | Min(0%, -100% + (1% to 5%) × Max(0, Base {{icon|miltech}}MilTech - 3.79) × 0.75 if [[Army Nuclear Hardening]] researched × 0.140625 if working for Aliens) || 50% chance for each Human army that is not Ally of Nuker<ref name=allyofnuker />.
|-
| colspan=2 | -100% × 0.75 if [[Army Nuclear Hardening]] researched × 0.140625 if working for Aliens || The other 50% chance for each Human army that is not Ally of Nuker<ref name=allyofnuker />.
|-
| colspan=2 | Min(0%, -100% + (1% to 5%) × Max(0, Base {{icon|miltech}}MilTech - 3.79)) || 50% chance for each Megafauna army.
|-
| colspan=2 | -100% || The other 50% chance for each [[Aliens#Megafauna|Megafauna]] army.
|-
| colspan=2 | -100% / (48 to 52) || For each army that is Ally of Nuker<ref name=allyofnuker />.
|-
| Each [[Councilors|Councilor]] in Target Region || colspan=2 | 50% Chance to die || [[Survivor]] trait gives immunity.
|-
| [[Aliens#Xenoforming|Alien Xenoforming]] || colspan=2 | Set to 0 Xenoflora Growth Levels || None
|-
| Add [[Climate Change|Aerosols]] || colspan=2 | 0.00777 || Multiply by Region Area (km²) / 10000km² if Region is an Island smaller than 10000km².
|-
| colspan=4 | Target Region Gains 1 Layer of Nuclear Fallout
|}

<references />

== Orbital Bombardment ==

[[Spaceships]] with certain weapon modules can bombard hostile armies from orbit.

See [[Fleets#Orbital_Bombardment]] for more details.

{{Mechanics_Navbox}}

Terrestrial Warfare

2026-03-17T19:43:59Z

76561197989421583: /* 1. Hit Chance (The Accuracy Gap) */ quick guide useless since I added the table just behind

This page mainly discusses the mechanics for fighting terrestrial wars. For a more detailed discussion about starting and ending wars, see [[Foreign Relations#Wars]] instead.

[[Foreign Relations#Wars|Wars]] begin when a [[Councilors|councilor]] for the executive [[Factions|faction]] of one of two [[Foreign Relations#Rivals|Rivals]] selects the [[Foreign Relations#Declaring_Wars|War policy]] against the rival. All war-capable [[Foreign Relations#Alliances|allies]] of the defending rival (with an army or nuclear weapons) join the war. All war-capable allies of the attacker are given the option to join on the attacker's side.

To win a war, an [[Nations#Armies|army]] must occupy the enemy's {{icon|capital|bgcolor=DarkSlateGray}}Capital [[Regions|region]]. At that moment, the war ends, triggering a [[Foreign Relations#War_Conquest|regime change]]. [[Foreign Relations#Claims|Claimed regions]] change hands to the occupier and its allies. If any of the invaded nation remains, its control point owners are replaced with those of the victor. Some of the nation's stats change when a new regime is installed, sometimes in unpredictable ways, but the new ruling faction will be able to fund [[Nations#Direct_Investment|Direct Investments]] into the nation at greatly reduced {{TV|influence}} cost for a period of one year. Unoccupied [[Regions]] and surviving enemy armies will contribute to greater {{TV|unrest}} following a regime change.

Wars may also end with a [[Foreign Relations#Seeking_Peace|simple peace]] where both sides return to the prewar status quo.

== Armies ==

[[Nations#Armies|Armies]] represent multiple modern divisions that are capable of gaining and holding territory in other [[Nations]]. Control of an army is gained after councilors gain at least partial control of a nation. Most [[Nations]] don't have armies at the campaign start, but [[Nations]] with sufficient {{TV|pop}} can build new ones with enough investment into the {{TV|build army}}. While powerful, armies are a drag on a nation's {{icon|ip|bgcolor=DarkSlateGray}}economic development and remain subject to the international relations of their home countries, which too can be managed with sufficient control of a nation.

Armies have a [[File:ICO army HQ.png|20px]]headquarters region in their home nation. If located there, they incur a smaller cost to the nation's {{icon|ip|bgcolor=DarkSlateGray}}economic development.

Armies rely on two key values: its parent nation's {{TV|miltech}} level and its strength. The strength value measures how much damage the army has taken. Armies usually passively and freely repair themselves when not fighting in a friendly region.

Some armies have a {{icon|navy}}[[Nations#Navies|Navy]] upgrade that allows them to transit oceans. During wartime, a nation's navies can only cross the water if the nation has naval superiority over its foes. Only larger or wealthier [[Nations]] have the capability to {{icon|build navy}}build and project power with {{icon|navy}}navies.

=== Naval Freedom ===

For each [[Foreign Relations#Wars|war]], the game computes for each side the sum of the {{TV|miltech}} of the armies that have a navy upgrade. If one side has a higher sum than the other, then the other side of the war is blockaded: all of its nations no longer have Naval Freedom.

As a result, a nation only has Naval Freedom if it is not blockaded in any of the wars that it is involved in.

Notably, since wars can get very messy, with multiple overlapping wars, it is actually entirely possible for all nations to lose their Naval Freedom.

Consider a simple example with 3 nations: A, B, and C, such that:
* A has a single navy with {{TV|miltech|3}}.
* B has a single navy with {{TV|miltech|2}}.
* C has a single navy with {{TV|miltech|2}}.

Suppose there are three overlapping wars X, Y, and Z, such that:
* War X pits A against B.
* War Y pits A against C.
* War Z pits A against B and C.

Then the result would be:
* War X blockades B, since A's 3 naval score beats B's 2 naval score.
* War Y blockades C, since A's 3 naval score beats C's 2 naval score.
* War Z blockades A, since A's 3 naval score is beaten by the combined naval score of B's 2 naval score added to C's 2 naval score = 4 naval score.

So all 3 nations have no Naval Freedom.

=== Army Movement ===

Armies are allowed to be in any region R such that one of the following is true:
* R belongs to the army's home nation.
* R belongs to a nation that is [[Foreign Relations#Alliances|allied]] to the army's home nation.
* R belongs to a nation that is [[Foreign Relations#Wars|at war]] with the army's home nation.

An army can directly travel from any region R1 to any region R2 such that at least one of the following is true:
* R1 and R2 are adjacent.<ref name=adjacent>Note: Certain research projects can make pairs of regions become adjacent.</ref>
* R1 and R2 are adjacent only for friendly armies<ref name=adjacent />, and both R1 and R2 belong to nation(s) that are not at war with the army's home nation.
* All of the following are true:
** R1 and R2 both currently have [[Regions#World_Ocean_Access|world ocean access]].
** The army's home nation has [[Terrestrial_Warfare#Naval_Freedom|naval freedom]].
** Either the army does not need to travel between the Black Sea and the World Ocean, or the army's home nation has access to the Turkish Strait.

A nation has Turkish Strait access as long as one of the following is true:
* It is not at war with the nation that owns the Istanbul region.
* The Istanbul region is fully occupied.

<references />

==== Land Movement ====

The time needed for an army to travel directly between two adjacent regions without using a navy is calculated as follows:
<pre> Duration (days) = Distance (km) / 300 (km/day) * 4 / Miltech </pre>

But this value is affected by the following multipliers:
{| class="wikitable sortable" style="text-align:center;"
|-
! rowspan=2| Condition(s) !! colspan=3|Multiplier Value When:
|-
! Only Origin Region is Small<ref name=small>A region is small if it is smaller than 150000km².</ref> !! Only Destination Region is Small<ref name=small />!! Otherwise
|-
| Origin Region is not friendly OR Origin Region has enemy armies || 5 ^ 0.2 || 5 ^ 0.8 || 5 ^ 0.5
|-
| (Origin Region is not friendly OR Origin Region has enemy armies) AND Origin Region is {{icon|rugged}}Rugged || 1.5 ^ 0.2 || 1.5 ^ 0.8 || 1.5 ^ 0.5
|-
| Origin Region is friendly AND Origin Region has no enemy armies AND Origin Region is {{icon|rugged}}Rugged || 1.25 ^ 0.2 || 1.25 ^ 0.8 || 1.25 ^ 0.5
|-
| Origin Region is friendly AND Origin Region has no enemy armies AND Origin Nation has {{TV|unrest|>5}} || (1 + (Origin Nation {{TV|unrest}} - 5) / 6.5) ^ 0.2 || (1 + (Origin Nation {{TV|unrest}} - 5) / 6.5) ^ 0.8 || (1 + (Origin Nation {{TV|unrest}} - 5) / 6.5) ^ 0.5
|-
| Origin Region is a {{icon|colony|bgcolor=DarkSlateGray}}Colony || 1.5 ^ 0.2 || 1.5 ^ 0.8 || 1.5 ^ 0.5
|-
| Destination Region is not friendly || 5 ^ 0.8 || 5 ^ 0.2 || 5 ^ 0.5
|-
| Destination Region is not friendly AND Destination Region is {{icon|rugged}}Rugged || 1.5 ^ 0.8 || 1.5 ^ 0.2 || 1.5 ^ 0.5
|-
| Destination Region is friendly AND Destination Region is {{icon|rugged}}Rugged || 1.25 ^ 0.8 || 1.25 ^ 0.2 || 1.25 ^ 0.5
|-
| Destination Region is friendly AND Destination Nation has {{TV|unrest|>5}} || (1 + (Destination Nation {{TV|unrest}} - 5) / 6.5) ^ 0.8 || (1 + (Destination Nation {{TV|unrest}} - 5) / 6.5) ^ 0.2 || (1 + (Destination Nation {{TV|unrest}} - 5) / 6.5) ^ 0.5
|-
| Destination Region is a {{icon|colony|bgcolor=DarkSlateGray}}Colony || 1.5 ^ 0.8 || 1.5 ^ 0.2 || 1.5 ^ 0.5
|}

<references />

==== Naval Movement ====

The time needed for an army to travel between two regions without using a navy is calculated as follows:
<pre> Duration (days) = (14 days + Distance (km) / 792 (km/day) ) * 4 / Miltech </pre>

But this value is affected by a number of complex calculations that consider the different possible sea routes. In particular, the duration can be significantly affected by whether the army's nation has access to the Suez and Panama canals.

A nation has canal access as long as one of the following is true:
* It is not at war with the nation that owns the Canal region.
* The Canal region is fully occupied.

The Canal regions are:
* Cairo for the Suez Canal.
* Panama City for the Panama Canal.

=== Army Battle ===

==== Simplified Combat Rules ====

Combat in ''Terra Invicta'' is a comparison of Miltech levels. Higher Miltech means you hit more often and deal more damage. If two forces have equal Miltech, the base hit chance is 50%.

===== 1. Hit Chance (The Accuracy Gap) =====
The game calculates the difference (Δ) between the Attacker's Miltech and the Defender's Miltech.

If Miltechs are equal: 50% Hit Chance.
If you have the advantage: Your hit chance climbs toward 100%.
If you are outclassed: Your hit chance drops toward 0%.

Hit Chance (Advantage)=100%−(50%×0.7751.5×Δ)
Hit Chance (Disadvantage)=50%×0.7751.5×Δ

====== Hit Chance Reference Table ======

The following table shows the 1vs1 hit chance based on the Miltech difference (Delta = Attacker Miltech - Defender Miltech).

{| class="wikitable" style="text-align: center;"
|-
! Miltech Difference (Delta) !! Hit Chance !! Note
|-
| '''+3.0''' || '''84.1%''' ||
|-
| '''+2.0''' || '''76.7%''' ||
|-
| '''+1.0''' || '''65.9%''' || '''Strong offensive edge.'''
|-
| +0.8 || 63.2% ||
|-
| +0.6 || 60.3% ||
|-
| +0.4 || 57.1% ||
|-
| +0.2 || 53.7% ||
|-
| '''0.0''' || '''50.0%''' || '''Even match; coin-flip odds.'''
|-
| -0.2 || 46.3% ||
|-
| -0.4 || 42.9% ||
|-
| -0.6 || 39.7% ||
|-
| -0.8 || 36.8% ||
|-
| '''-1.0''' || '''34.1%''' || '''Struggling to land hits.'''
|-
| '''-2.0''' || '''23.3%''' ||
|-
| '''-3.0''' || '''15.9%''' ||
|}

===== 2. Damage Formulas =====
Damage is calculated as a percentage of the defender’s Max Health.

====== Army vs. Army ======
When an army hits another army, it '''deals roughly 10% of its Miltech in percentage of defender’s Max Health'''.

Base Damage: Miltech × 0.1 (±20%)

Variance: ±20% is the game simulating a damage range mechanic.

Critical Hit: Usually 1x. Increases to 3x if the attacker is at full health and the region is unoccupied (an "Ambush"), or by a small random chance based on the total number of armies in the fight.

====== Region vs. Army ======
Region defenses (fortifications/militia) '''fire every day at every hostile army'''. They deal less base damage but have much higher "Critical" lethality.

Base Damage: Region Miltech × 0.0225

The "Lethality" Multiplier: If an army is at full health and the region is unoccupied, the region can deal a massive 100x damage critical hit.

Overwhelmed Defenses: If more hostile armies are present than friendly armies, the region's damage output is reduced.

====== Occupying a Region (Army vs. Region) ======
When an army hits region defenses, it increases the Occupation %.

Base Damage: Army Miltech × 0.0225

Advantage Bonus: If your Army Miltech is higher than the region's base tech, you gain occupation faster.

Geography Modifiers: Occupation is slower in regions with huge populations (like Delhi) or massive land areas (like Siberia).

Crowding Penalty: Having too many armies in one spot (more than 1 per 100,000 km2) slows down occupation by up to 50%.

==== Combat Rules ====

Combat occurs whenever an army A is in a [[Regions|region]] R such that at least one of the following is true:
* A's home nation is [[Foreign_Relations#Wars|at war]] with the home nation of another army in R.
* R is partially or fully occupied and A's home nation owns R.
* R is partially or fully occupied and A's home nation is [[Foreign_Relations#Alliances|allies]] with the nation that owns R.
* A's home nation is [[Foreign_Relations#Wars|at war]] with the nation that owns R and R is not fully occupied.
* A's home nation does not exist and R is not fully occupied.
{{SpoilerBox|Alien-Related}}
* There is a [[Aliens#Megafauna|Megafauna Army]] in R that is not owned by the same faction that owns A.
* A's home nation is [[Foreign_Relations#Wars|at war]] with the nation that owns R and A is an [[Aliens#Invader_Armies|Invader Army]] and R is fully occupied by a war alliance that does not include the [[Aliens#Alien_Administration|Alien Nation]].
* A's home nation does not exist and A is an [[Aliens#Invader_Armies|Invader Army]] and R is fully occupied by a war alliance that does not include the [[Aliens#Alien_Administration|Alien Nation]].
* A is a [[Aliens#Megafauna|Megafauna Army]] that is owned by the {{icon|alien}}[[Aliens]] and R is not part of the [[Aliens#Alien_Administration|Alien Nation]] and R is not owned by a nation whose executive is controlled by a faction that has researched [[Xenofauna Harmony]].
* A is a [[Aliens#Megafauna|Megafauna Army]] that is owned by a faction F that is '''not''' the {{icon|alien}}[[Aliens]] and every non-[[Aliens#Megafauna|Megafauna]] army in R that is owned by F is owned by a nation that is [[Foreign_Relations#Wars|at war]] with the nation that owns R.
{{SpoilerBoxEnd}}

Combat is simulated as a daily exchange of attacks. For each army A:
# If there is an enemy army in the combat region, then A randomly selects one to fire at, preferring to avoid any armies owned by the same faction as A.
# If A is within a region that is hostile to A, then the region defenses fires at A.
# If A did not fire at anyone in the first step AND the region defenses missed its attack on A, then A fires at the region defenses.

Note that this means every army can fire at most one attack per day, but region defenses fire an attack on every hostile army every day.

Every attack has a hit chance that is determined by the gap between the attacker's {{TV|miltech}} and the defender's {{TV|miltech}}. But several modifiers may be applied to each side's {{TV|miltech}}, including but not limited to {{MissionIcon|Advise}}[[Advise|Advising]] [[Councilors]], {{icon|rugged}}rugged terrain bonuses, and damage taken.

When attacks hit, damage is taken, which scales based on the attacker's {{TV|miltech}}. When armies take damage, their health % drops. When region defenses take damage, their occupation % increases.

If a region is fully occupied it ceases fighting, but it can't change hands until the war is concluded. Regional economies and space facilities can take significant [[Regions#Region_Damage|collateral damage]] during fighting, although the rate of damage goes down as {{{TV|miltech}} goes up (representing more precise weaponry). Sufficient collateral damage will count as an [[Factions#Atrocity|atrocity]] by the army's owning faction.

==== Formulas ====

'''Miltech Calculations:'''

{| class="wikitable"
|-
! Factor !! Army Miltech A !! Army Miltech B !! Region Miltech
|-
| Base Miltech || Base Miltech || Base Miltech || Base Miltech
|-
| Councilor {{MissionIcon|Advise}}[[Advise]] Bonus || +0.01 per {{TVS|command}} || +0.01 per {{TVS|command}} || +0.01 per {{TVS|command}}
|-
| LEO Hab Bonus (capped at +0.3) || +0.03 per Military Lab || +0.03 per Military Lab || No Effect
|-
| In Home Nation || +0.2 || +0.2 || No Effect
|-
| In Home Nation AND region is {{icon|rugged}}rugged || +0.2 || +0.2 || +0.2
|-
| In Home Nation AND region is {{icon|core economic region|bgcolor=DarkSlateGray}}core economic || +0.1 || +0.1 || +0.1
|-
| Region is {{icon|rugged}}rugged and [[Mountain Warfare Doctrine]] is researched || +0.125 || +0.125 || +0.125
|-
| Region is {{icon|core economic region|bgcolor=DarkSlateGray}}core economic and [[Urban Warfare Doctrine]] is researched || +0.125 || +0.125 || +0.125
|-
| Army CP is disabled (Abandoned or {{MissionIcon|Crackdown}}[[Crackdown]]ed) || -0.2 || -0.2 || No Effect
|-
| In Allied (or Home) Nation || +0.05 per {{TV|cohesion}} of Allied Nation || No Effect || No Effect
|-
| Home Nation's {{TV|cohesion}} || No Effect || No Effect || +0.05 per {{TV|cohesion}}
|-
| Home Nation's {{TV|unrest}} || No Effect || No Effect || -0.05 per {{TV|unrest}}
|-
| Adjacent Regions belonging to Same Home Nation || No Effect || No Effect || +Fraction of such Regions that are unoccupied and not fighting × Home Nation's Miltech × 0.1 × (1 - 0.05 × Home Nation's {{TV|unrest}})
|-
| Remaining Combat Effectiveness || × (1 - 0.5 × Lost Health %) || × (1 - 0.5 × Lost Health %) || × (1 - 1/3 × Occupation %)
|-
|}

Note: If a nation has not completed the {{TV|found military}}, then its regions have effectively {{TV|miltech|0}} for combat.

'''Hit Chance Calculation:'''
* When an army fires at another army, the attacking army uses its '''Army Miltech A''' as the Attack value, while the defending army uses its '''Army Miltech B''' as the Defense value.
* When region defenses fire at an army, the region defenses use '''Region Miltech''' as the Attack value, while the defending army uses its '''Army Miltech A''' as the Defense value.
* When an army fires at the region defenses, the hit chance is always '''100%'''. (But the army only fires if the region defenses missed their attack.)

{| class="wikitable"
|-
! Condition
! Formula
|-
| Defense ≥ Attack
| <code>50% × 0.775^(1.5 × (Defense-Attack))</code>
|-
| Attack > Defense
| <code>100% − (50% × 0.775^(1.5 × (Attack-Defense)))</code>
|}

'''Damage taken:'''
When an army successfully lands a hit on another army, the defending army loses X% of its max health, where X calculated as follows:
# Set X to the attacking army's '''Army Miltech A'''.
# Multiply X by 0.1.
# Multiply X by a random value between 0.8 and 1.2.
# Multiply X by a critical multiplier Z, calculated as follows:
## Set Z to 1.
## Y% chance to set Z to 3, where Y is the square of the number of armies in the region that are involved in the war (allied armies that aren't part of the war don't count).
## If the attacking army is at full health and neither army is a [[Aliens#Megafauna|Megafauna]] and the region is 0% occupied, set Z to 3.
# All army damage bonuses from [[Technology|Projects]] are applied to X. (These bonuses are multiplicative and compounding, but often require the defending army to be a specific type of army.)

When the region defenses successfully land a hit on an army, the defending army loses X% of its max health, where X calculated as follows:
# Set X to the region's '''Region Miltech'''.
# Multiply X by 0.0225.
# Multiply X by a random value between 0.8 and 1.2.
# Let Y be the number of region-friendly armies in the region that are involved in the war (allied armies that aren't part of the war don't count) multiplied by the square of the number of region-hostile armies in the region.
# Multiply X by a critical multiplier Z, calculated as follows:
## Set Z to 1.
## Y% chance to set Z to 40.
## If the region is 0% occupied and the defending army is at full health, then set Z to 100.
## If Z is not 100, another Y% chance to set Z to 40.
## If Z is less than 40, (Y% / (100% - Y%)) chance to set Z to 5.
# All army damage bonuses from [[Technology|Projects]] are applied to X, except for bonuses against [[Aliens#Megafauna|Megafauna]]. (These bonuses are multiplicative and compounding, but often require the defending army to be a specific type of army.)
# Let H be the sum of the Remaining Combat Effectiveness multipliers of every region-hostile army in the region.
# Let F be the sum of the Remaining Combat Effectiveness multipliers of every region-friendly army in the region that is involved in the war (allied armies that aren't part of the war don't count).
# If H - F is more than 0, then multiply X by 1 - (H - F) / (H - F + 2).
# (1 - Region occupation % by defending army's home nation / H) chance to multiply X by 2.

If this last (1 - Region occupation % by defending army's home nation / H) chance fails, the region occupation % by the defending army's home nation actually '''decreases''' by D%, where D is calculated as follows:
# Set D to the region's Region Miltech.
# Multiply D by 0.0225.
# Multiply D by a random value between 0.8 and 1.2.
# Divide D by the number of region-hostile armies in the region.
# Multiply D by the '''Region Combat Action Multiplier''', which is calculated as 2 / (Region Population ^ 0.75 / Game Start Mean Average Region Population ^ 0.75 + Region Area ^ 0.5 / Median Region Area ^ 0.5).
# If D > 10, then set D to 10.

When an army hits the region defenses, the attacking army's home nation increases its occupation % of the region by X%, where X is calculated as follows:
# Set X to the attacking army's '''Army Miltech A'''.
# Let G be X - the defending region's home nation's base {{TV|miltech}} - the Councilor {{MissionIcon|Advise}}[[Advise]] Bonus for the defending region's home nation.
# If G > 0 then add G to X.
# Multiply X by 0.0225.
# Multiply X by a random value between 0.8 and 1.2.
# Multiply X by the '''Region Combat Action Multiplier''', which is calculated as 2 / (Region Population ^ 0.75 / Game Start Mean Average Region Population ^ 0.75 + Region Area ^ 0.5 / Median Region Area ^ 0.5).
# Multiply X by a critical multiplier Z, calculated as follows:
## Set Z to 1.
## Y% chance to set Z to 40.
## If the region is 0% occupied and the defending army is at full health, then set Z to 100.
## If Z is not 100, another Y% chance to set Z to 40.
## If Z is less than 40, (Y% / (100% - Y%)) chance to set Z to 5.
# Let C be the number of region-hostile armies in the region - the region area / 100000km².
# If C > 0, then multiply X by Max(1 - C * 0.02, 0.5)
# If X > 10, then set X to 10.

=== Army Operations ===
The faction that controls an army can conduct operations with it. They are:
{| class="wikitable"
! Operation !! width=85% | Effects
|-
| [[File:ICO DeployArmyOperation on.png|40px]] Deploy Army
| Move this Army to an adjacent region, including those of allies or wartime enemies. Armies will engage in battle with enemy armies and occupy enemy regions.
|-
| [[File:ICO DeployArmiesOperation on.png|40px]] Deploy Armies
| Move all stacked armies to an adjacent region, including those of allies or wartime enemies. Armies will engage in battle with enemy armies and occupy enemy regions.
|-
| [[File:ICO AssaultAlienAssetOperation on.png|40px]] Assault Alien Asset
| Launch an assault on a fixed alien target.
|-
| [[File:ICO AssaultSpaceFacilityOperation on.png|40px]] Assault Space Facility
| Destroy a fixed space facility in the region.
|-
| [[File:ICO RazeRegionOperation on.png|40px]] Raze Region
| Launch a general attack on economic and civilian targets in this region. Commits 5 to 25 [[Factions#Atrocity|atrocities]].
|-
| [[File:ICO ArmyGoHomeOperation on.png|40px]] Airlift Home
| Return this army to its home region during peacetime. Operation will not complete if home nation is at war.
|-
| [[File:ICO CancelArmyOperation on.png|40px]] Cancel Operation
| Cancel current operation for this Army. Army will resume fighting if enemies are present.
|}

'''Wiki Help wanted''': Look up the in-game image and description for the Army Annex Region operation and upload both here!

==== Annex Region ====

The game mechanics for army annex operations are explained here [[Foreign Relations#War_Annexation]].

==== Raze Region ====

See [[Regions#Region_Damage]].

==== Assault Alien Asset ====

{| class="wikitable"
|+ Damage Taken by {{TV|armies}} when they Assault Alien Assets
|-
! rowspan=2 | Mission Outcome !! colspan=2 | Type of Alien Asset
|-
! [[Aliens#Alien_Xenoforming|Xenoflora]] !! Other
|-
| Critical Failure || (30% to 150%) / Base {{TV|miltech}} || (150% to 300%) / Base {{TV|miltech}}
|-
| Normal Failure || (15% to 112.5%) / Base {{TV|miltech}} || (75% to 225%) / Base {{TV|miltech}}
|-
| Normal Success || (0% to 75%) / Base {{TV|miltech}} || (0% to 150%) / Base {{TV|miltech}}
|-
| Critical Success || (0% to 15%) / Base {{TV|miltech}} || (0% to 30%) / Base {{TV|miltech}}
|}

Note: Base {{TV|miltech}} is simply the army's home nation's {{TV|miltech}}, with all modifiers ignored.

See [[Aliens]] for spoilers on the different types of alien assets that can be assaulted, as well as the consequences of such assaults.

=== Army Healing ===

An injured human army will passively heal over time when all of the following conditions are true:
* It is in a friendly region<ref>A region owned by its home nation or a nation allied to its home nation</ref>.
* The region is currently not occupied or being occupied.
* It is not in battle with other armies.
* It is not currently performing an operation.

The % health that gets healed each day is calculated as follows:
# 0.5% Base.
# +0.5% more if the faction that controls the army also controls the [[Nations#Control_Point_Types|Defense Sector Control Point]] of the army's home nation.
# +0.5% more if the army is in its home nation.
# +0.5% more if the army is in its home region.
# Multiply the total by (1 - (Currently Healing Human Armies of Home Nation / (Total Human Armies of Home Nation + 1))).
#* Note: This step is currently bugged to never occur.
# +0.5% more if the faction that controls the army has researched the [[Rapid Repairing Materials]] project.
# +0.5% more if the faction that controls the army has researched the [[Predictive Logistics Systems]] project.

{{SpoilerBox|Alien-Related}}
Human armies that are owned by the {{icon|alien}}[[Aliens]] still follow the same healing rules.

But for the healing mechanics of Alien-related armies, see [[Aliens#Megafauna]] and [[Aliens#Invader_Armies]] instead.
{{SpoilerBoxEnd}}

<references />

=== Army Death ===

Whenever an army dies, multiple effects may occur:

==== Democracy Penalties ====

If the dead army belonged to a democratic human nation, then that nation suffers two penalties:
* A {{TV|cohesion}} loss equal to the nation's {{TV|democracy}} / 10.
* Applies [[Nations#Changing_Public_Opinion|Propaganda]] in the nation for the faction that owned the dead army. Propaganda strength is equal to (0 - the nation's {{TV|democracy}}).

==== Army IP Refund ====

Whenever a human army dies, its home [[Nations|nation]] receives a fraction of its {{TV|IP}} Cost as a refund. This refund is put directly into the {{TV|build army}} and/or {{TV|build navy}}, so it can often result in new {{TV|armies}} and/or {{TV|navies}} being built the next day. Specifically, the refund amounts are calculated as follows:

{| class="wikitable sortable" style="text-align:center;"
|+ Refund Amounts for {{TV|build army}}. Only applies if army did not die by nuke.
|-
! Army Died in Home Nation? !! Refund Amount
|-
| Yes || (30% to 50%) of {{TV|build army}} cost.
|-
| No || (15% to 25%) of {{TV|build army}} cost.
|}

{| class="wikitable sortable" style="text-align:center;"
|+ Refund Amounts for {{TV|build navy}}. Only applies if the dead army had a navy.
|-
! Army Died in Home Nation? !! Home Nation has [[Terrestrial_Warfare#Naval_Freedom|Naval Freedom]]? !! Army Died in Region that currently has [[Regions#World_Ocean_Access|World Ocean Access]]? !! Refund Amount
|-
| Yes || Yes || Yes || (70% to 90%) of {{TV|build navy}} cost.
|-
| Yes || Yes || No || (90% to 110%) of {{TV|build navy}} cost.
|-
| Yes || No || || (20% to 30%) of {{TV|build navy}} cost.
|-
| No || Yes || Yes || (60% to 80%) of {{TV|build navy}} cost.
|-
| No || Yes || No || (80% to 100%) of {{TV|build navy}} cost.
|-
| No || No || || (10% to 20%) of {{TV|build navy}} cost.
|}

==== Complete Milestones ====

If the army is related to the [[Aliens]] in any way, then the faction that kills it may achieve certain milestones from doing so. See [[Aliens]] for details.

==== Hate Vent ====

See [[Diplomacy#Alien_Hate_Vent]].

== Nuclear Warfare ==
Some nations have a number of {{TV|nukes}} available to them. These represent launching multiple strategic nuclear weapons at a target region. Launching nuclear strikes will devastate the economy of a [[Regions|region]] and the enemy {{TV|armies}} within it, although the damage will be somewhat mitigated if a nation is launching strikes on its own or an [[Foreign_Relations#Alliances|ally]]'s territory. Launching factions will be charged with committing one or more [[Factions#Atrocity|atrocities]]. Detonating a sufficient number of nuclear weapons may also have disastrous global effects. A region with {{icon|sto defense}}space defenses cannot be attacked with {{TV|nuke}}.

Nations can develop nuclear weapon with the {{TV|develop atomic bomb}}, which also gives {{TV|nuke|1}}. A nation with nuclear weapon program can build more with the {{TV|nuclear weapons}}.

Nations construct nuclear weapons as a deterrent to enemy invasion. Attempting to conquer a nuclear-armed nation will almost certainly lead to nuclear strikes in retaliation.

=== Valid Targets for a Nuclear Strike ===

Nukes can only be fired at [[Regions]]. The set of regions that a [[Nations|nation]] X can fire a nuke at is computed as follows:
# Add every region that is owned by any nation that is [[Foreign_Relations#Wars|at war]] with X.
# If X does not have a spaceflight program, then remove every region that is not adjacent to X and does not have [[Regions#World_Ocean_Access|ocean access]].
# If X does not have a spaceflight program and does not have [[Terrestrial_Warfare#Naval_Freedom|naval freedom]], then remove every region that is not adjacent to X.
# Add every region owned by X or an [[Foreign_Relations#Alliances|ally]] of X if the region currently contains an army that is owned by any nation that is [[Foreign_Relations#Wars|at war]] with X.
# For every region R, remove R unless one of the following is true:
#* R is owned by X.
#* R is owned by an [[Foreign_Relations#Alliances|ally]] of X.
#* R is owned by a nation that is [[Foreign_Relations#Wars|at war]] with X and R does not have a [[Nations#Space_Defenses|space defense facility]] built.

=== Effects of a Nuclear Strike ===

Launching nuclear weapons will do terrible and lasting damage to the targeted region, destroy any enemy {{TV|armies}} and all space facilities, and surely be seen with horror around the globe.

{| class="wikitable"
|+ Effects of a Nuclear Attack (In Chronological Order)
|-
! Category !! Amount for Offensive Nukes !! Amount for Defensive Nukes !! Modifiers
|-
| Target [[Nations#GDP_Per_Region|Region GDP]] || -52.5% to -87.5% || -15% to -25%
| rowspan=2 |
* [[Urban Armoring]] multiplies amount by 0.8.
* [[Civil Defense Programs]] multiplies amount by 0.8.
|-
| Target {{icon|pop}}[[Nations#Population|Region Population]] || -18.75% to -31.25% || -1.875% to -3.125%
|-
| Target Nation [[Nations#Sustainability|Pollution Multiplier]] || +0.075 to +0.125 || +0.00375 to +0.00625 || Multiplied by [[Nations#GDP_Per_Region|Region GDP]] / [[Nations#GDP|Nation GDP]]
|-
| Nuking Faction Commits [[Factions#Atrocity|Atrocities]] || colspan=2 | 1 per 100k {{TV|pop}} killed (rounded down).
|
* Multiply by 10 if nuke launcher is not on the defending side of any war where the target nation is on the attacking side.
** ...seems to apply for self-nukes too??
{{SpoilerBox|Alien-Related}}
** Does not apply if the target region is owned by the [[Aliens#Alien_Administration|Alien Nation]].
{{SpoilerBoxEnd}}
* Capped between 1 and 20.
|-
| All Human Nations' GDP || -25% × [[Nations#GDP_Per_Region|Region GDP]] / Global GDP + (0% to -2%) || -5% × [[Nations#GDP_Per_Region|Region GDP]] / Global GDP + (0% to -2%) || None
|-
| [[Family Ties]] Trait Effect || colspan=2 | {{TV|loyalty|-10}} || Multiply by 2 if Councilor's Faction launched the nuke.
|-
| Target Region is {{icon|core economic region|bgcolor=DarkSlateGray}}Core Economic || Remove {{icon|core economic region|bgcolor=DarkSlateGray}}Core Economic status || Nothing || None
|-
| All Human Nations' [[Nations#GDP|GDP]] || -2.5% + (0% to -2%) || N/A || If Target Region just lost {{icon|core economic region|bgcolor=DarkSlateGray}}Core Economic status.
|-
| Target Region is {{icon|oil region}}Core Oil or {{icon|resource region}}Core Mining || Remove {{icon|oil region}}Core Oil or {{icon|resource region}}Core Mining status || Nothing || None
|-
| All Human Nations' [[Nations#GDP|GDP]] || -1.5% + (0% to -2%) || N/A || If Target Region just lost {{icon|oil region}}Core Oil or {{icon|resource region}}Core Mining status.
|-
| Target Nation [[Nations#Priorities|Priorities]] || colspan=2| Set to 0 || Except {{icon|spoils}}Spoils, {{icon|unity}}Unity, and {{icon|oppression}}Oppression.
|-
| rowspan=2 | Destroy Space Assets in Target Region || colspan=2 | All {{icon|boost}}[[Nations#Boost|Boost]], {{icon|mc}}[[Nations#Mission_Control|Mission Control]] , and {{icon|sto defense|bgcolor=DarkSlateGray}}[[Nations#Space_Defenses|Space Defenses]] || If Target Nation is NOT Nuke Launcher
|-
| N/A || All {{icon|boost}}[[Nations#Boost|Boost]] and {{icon|sto defense|bgcolor=DarkSlateGray}}[[Nations#Space_Defenses|Space Defenses]], just 1 {{icon|mc}}[[Nations#Mission_Control|Mission Control]] || If Target Nation is Nuke Launcher
|-
| Target Nation {{icon|funding}}[[Nations#Funding|Funding]] || N/A || -50% × [[Nations#GDP_Per_Region|Region GDP]] / [[Nations#GDP|Nation GDP]] || If Target Nation is Nuke Launcher
|-
| rowspan=7 | Health of Each Army in Target Region || colspan=2 | Instant Death || For the Strongest<ref>The strongest army is the army whose health % × Base {{TV|miltech}} is the highest.</ref> Army that is not Ally of Nuker<ref name=allyofnuker>An army is an ally of the nuker if any of the following are true:
* The army is owned by the nuking nation.
* The army is owned by an ally of the nuking nation.
* The army is owned by the nuking faction and not a [[Aliens#Megafauna|Megafauna]].</ref>.
|-
| colspan=2 | Min(0%, (-100% + (1% to 5%) × (Base {{icon|miltech}}MilTech - 3.79)) × 0.140625) || For each [[Aliens#Invader Armies|Alien Invader Army]] that is not Ally of Nuker<ref name=allyofnuker />.
|-
| colspan=2 | Min(0%, -100% + (1% to 5%) × Max(0, Base {{icon|miltech}}MilTech - 3.79) × 0.75 if [[Army Nuclear Hardening]] researched × 0.140625 if working for Aliens) || 50% chance for each Human army that is not Ally of Nuker<ref name=allyofnuker />.
|-
| colspan=2 | -100% × 0.75 if [[Army Nuclear Hardening]] researched × 0.140625 if working for Aliens || The other 50% chance for each Human army that is not Ally of Nuker<ref name=allyofnuker />.
|-
| colspan=2 | Min(0%, -100% + (1% to 5%) × Max(0, Base {{icon|miltech}}MilTech - 3.79)) || 50% chance for each Megafauna army.
|-
| colspan=2 | -100% || The other 50% chance for each [[Aliens#Megafauna|Megafauna]] army.
|-
| colspan=2 | -100% / (48 to 52) || For each army that is Ally of Nuker<ref name=allyofnuker />.
|-
| Each [[Councilors|Councilor]] in Target Region || colspan=2 | 50% Chance to die || [[Survivor]] trait gives immunity.
|-
| [[Aliens#Xenoforming|Alien Xenoforming]] || colspan=2 | Set to 0 Xenoflora Growth Levels || None
|-
| Add [[Climate Change|Aerosols]] || colspan=2 | 0.00777 || Multiply by Region Area (km²) / 10000km² if Region is an Island smaller than 10000km².
|-
| colspan=4 | Target Region Gains 1 Layer of Nuclear Fallout
|}

<references />

== Orbital Bombardment ==

[[Spaceships]] with certain weapon modules can bombard hostile armies from orbit.

See [[Fleets#Orbital_Bombardment]] for more details.

{{Mechanics_Navbox}}

Terrestrial Warfare

2026-03-17T19:41:30Z

76561197989421583: /* Region vs. Army */ small improvement to readability, highlight important info

This page mainly discusses the mechanics for fighting terrestrial wars. For a more detailed discussion about starting and ending wars, see [[Foreign Relations#Wars]] instead.

[[Foreign Relations#Wars|Wars]] begin when a [[Councilors|councilor]] for the executive [[Factions|faction]] of one of two [[Foreign Relations#Rivals|Rivals]] selects the [[Foreign Relations#Declaring_Wars|War policy]] against the rival. All war-capable [[Foreign Relations#Alliances|allies]] of the defending rival (with an army or nuclear weapons) join the war. All war-capable allies of the attacker are given the option to join on the attacker's side.

To win a war, an [[Nations#Armies|army]] must occupy the enemy's {{icon|capital|bgcolor=DarkSlateGray}}Capital [[Regions|region]]. At that moment, the war ends, triggering a [[Foreign Relations#War_Conquest|regime change]]. [[Foreign Relations#Claims|Claimed regions]] change hands to the occupier and its allies. If any of the invaded nation remains, its control point owners are replaced with those of the victor. Some of the nation's stats change when a new regime is installed, sometimes in unpredictable ways, but the new ruling faction will be able to fund [[Nations#Direct_Investment|Direct Investments]] into the nation at greatly reduced {{TV|influence}} cost for a period of one year. Unoccupied [[Regions]] and surviving enemy armies will contribute to greater {{TV|unrest}} following a regime change.

Wars may also end with a [[Foreign Relations#Seeking_Peace|simple peace]] where both sides return to the prewar status quo.

== Armies ==

[[Nations#Armies|Armies]] represent multiple modern divisions that are capable of gaining and holding territory in other [[Nations]]. Control of an army is gained after councilors gain at least partial control of a nation. Most [[Nations]] don't have armies at the campaign start, but [[Nations]] with sufficient {{TV|pop}} can build new ones with enough investment into the {{TV|build army}}. While powerful, armies are a drag on a nation's {{icon|ip|bgcolor=DarkSlateGray}}economic development and remain subject to the international relations of their home countries, which too can be managed with sufficient control of a nation.

Armies have a [[File:ICO army HQ.png|20px]]headquarters region in their home nation. If located there, they incur a smaller cost to the nation's {{icon|ip|bgcolor=DarkSlateGray}}economic development.

Armies rely on two key values: its parent nation's {{TV|miltech}} level and its strength. The strength value measures how much damage the army has taken. Armies usually passively and freely repair themselves when not fighting in a friendly region.

Some armies have a {{icon|navy}}[[Nations#Navies|Navy]] upgrade that allows them to transit oceans. During wartime, a nation's navies can only cross the water if the nation has naval superiority over its foes. Only larger or wealthier [[Nations]] have the capability to {{icon|build navy}}build and project power with {{icon|navy}}navies.

=== Naval Freedom ===

For each [[Foreign Relations#Wars|war]], the game computes for each side the sum of the {{TV|miltech}} of the armies that have a navy upgrade. If one side has a higher sum than the other, then the other side of the war is blockaded: all of its nations no longer have Naval Freedom.

As a result, a nation only has Naval Freedom if it is not blockaded in any of the wars that it is involved in.

Notably, since wars can get very messy, with multiple overlapping wars, it is actually entirely possible for all nations to lose their Naval Freedom.

Consider a simple example with 3 nations: A, B, and C, such that:
* A has a single navy with {{TV|miltech|3}}.
* B has a single navy with {{TV|miltech|2}}.
* C has a single navy with {{TV|miltech|2}}.

Suppose there are three overlapping wars X, Y, and Z, such that:
* War X pits A against B.
* War Y pits A against C.
* War Z pits A against B and C.

Then the result would be:
* War X blockades B, since A's 3 naval score beats B's 2 naval score.
* War Y blockades C, since A's 3 naval score beats C's 2 naval score.
* War Z blockades A, since A's 3 naval score is beaten by the combined naval score of B's 2 naval score added to C's 2 naval score = 4 naval score.

So all 3 nations have no Naval Freedom.

=== Army Movement ===

Armies are allowed to be in any region R such that one of the following is true:
* R belongs to the army's home nation.
* R belongs to a nation that is [[Foreign Relations#Alliances|allied]] to the army's home nation.
* R belongs to a nation that is [[Foreign Relations#Wars|at war]] with the army's home nation.

An army can directly travel from any region R1 to any region R2 such that at least one of the following is true:
* R1 and R2 are adjacent.<ref name=adjacent>Note: Certain research projects can make pairs of regions become adjacent.</ref>
* R1 and R2 are adjacent only for friendly armies<ref name=adjacent />, and both R1 and R2 belong to nation(s) that are not at war with the army's home nation.
* All of the following are true:
** R1 and R2 both currently have [[Regions#World_Ocean_Access|world ocean access]].
** The army's home nation has [[Terrestrial_Warfare#Naval_Freedom|naval freedom]].
** Either the army does not need to travel between the Black Sea and the World Ocean, or the army's home nation has access to the Turkish Strait.

A nation has Turkish Strait access as long as one of the following is true:
* It is not at war with the nation that owns the Istanbul region.
* The Istanbul region is fully occupied.

<references />

==== Land Movement ====

The time needed for an army to travel directly between two adjacent regions without using a navy is calculated as follows:
<pre> Duration (days) = Distance (km) / 300 (km/day) * 4 / Miltech </pre>

But this value is affected by the following multipliers:
{| class="wikitable sortable" style="text-align:center;"
|-
! rowspan=2| Condition(s) !! colspan=3|Multiplier Value When:
|-
! Only Origin Region is Small<ref name=small>A region is small if it is smaller than 150000km².</ref> !! Only Destination Region is Small<ref name=small />!! Otherwise
|-
| Origin Region is not friendly OR Origin Region has enemy armies || 5 ^ 0.2 || 5 ^ 0.8 || 5 ^ 0.5
|-
| (Origin Region is not friendly OR Origin Region has enemy armies) AND Origin Region is {{icon|rugged}}Rugged || 1.5 ^ 0.2 || 1.5 ^ 0.8 || 1.5 ^ 0.5
|-
| Origin Region is friendly AND Origin Region has no enemy armies AND Origin Region is {{icon|rugged}}Rugged || 1.25 ^ 0.2 || 1.25 ^ 0.8 || 1.25 ^ 0.5
|-
| Origin Region is friendly AND Origin Region has no enemy armies AND Origin Nation has {{TV|unrest|>5}} || (1 + (Origin Nation {{TV|unrest}} - 5) / 6.5) ^ 0.2 || (1 + (Origin Nation {{TV|unrest}} - 5) / 6.5) ^ 0.8 || (1 + (Origin Nation {{TV|unrest}} - 5) / 6.5) ^ 0.5
|-
| Origin Region is a {{icon|colony|bgcolor=DarkSlateGray}}Colony || 1.5 ^ 0.2 || 1.5 ^ 0.8 || 1.5 ^ 0.5
|-
| Destination Region is not friendly || 5 ^ 0.8 || 5 ^ 0.2 || 5 ^ 0.5
|-
| Destination Region is not friendly AND Destination Region is {{icon|rugged}}Rugged || 1.5 ^ 0.8 || 1.5 ^ 0.2 || 1.5 ^ 0.5
|-
| Destination Region is friendly AND Destination Region is {{icon|rugged}}Rugged || 1.25 ^ 0.8 || 1.25 ^ 0.2 || 1.25 ^ 0.5
|-
| Destination Region is friendly AND Destination Nation has {{TV|unrest|>5}} || (1 + (Destination Nation {{TV|unrest}} - 5) / 6.5) ^ 0.8 || (1 + (Destination Nation {{TV|unrest}} - 5) / 6.5) ^ 0.2 || (1 + (Destination Nation {{TV|unrest}} - 5) / 6.5) ^ 0.5
|-
| Destination Region is a {{icon|colony|bgcolor=DarkSlateGray}}Colony || 1.5 ^ 0.8 || 1.5 ^ 0.2 || 1.5 ^ 0.5
|}

<references />

==== Naval Movement ====

The time needed for an army to travel between two regions without using a navy is calculated as follows:
<pre> Duration (days) = (14 days + Distance (km) / 792 (km/day) ) * 4 / Miltech </pre>

But this value is affected by a number of complex calculations that consider the different possible sea routes. In particular, the duration can be significantly affected by whether the army's nation has access to the Suez and Panama canals.

A nation has canal access as long as one of the following is true:
* It is not at war with the nation that owns the Canal region.
* The Canal region is fully occupied.

The Canal regions are:
* Cairo for the Suez Canal.
* Panama City for the Panama Canal.

=== Army Battle ===

==== Simplified Combat Rules ====

Combat in ''Terra Invicta'' is a comparison of Miltech levels. Higher Miltech means you hit more often and deal more damage. If two forces have equal Miltech, the base hit chance is 50%.

===== 1. Hit Chance (The Accuracy Gap) =====
The game calculates the difference (Δ) between the Attacker's Miltech and the Defender's Miltech.

If Miltechs are equal: 50% Hit Chance.
If you have the advantage: Your hit chance climbs toward 100%.
If you are outclassed: Your hit chance drops toward 0%.

Hit Chance (Advantage)=100%−(50%×0.7751.5×Δ)
Hit Chance (Disadvantage)=50%×0.7751.5×Δ

'''Quick Guide:''' A 1-point Miltech advantage raises your hit chance to roughly 66%. A 2-point advantage raises it to roughly 79%.
====== Hit Chance Reference Table ======

The following table shows the 1vs1 hit chance based on the Miltech difference (Delta = Attacker Miltech - Defender Miltech).

{| class="wikitable" style="text-align: center;"
|-
! Miltech Difference (Delta) !! Hit Chance !! Note
|-
| '''+3.0''' || '''84.1%''' ||
|-
| '''+2.0''' || '''76.7%''' ||
|-
| '''+1.0''' || '''65.9%''' || '''Strong offensive edge.'''
|-
| +0.8 || 63.2% ||
|-
| +0.6 || 60.3% ||
|-
| +0.4 || 57.1% ||
|-
| +0.2 || 53.7% ||
|-
| '''0.0''' || '''50.0%''' || '''Even match; coin-flip odds.'''
|-
| -0.2 || 46.3% ||
|-
| -0.4 || 42.9% ||
|-
| -0.6 || 39.7% ||
|-
| -0.8 || 36.8% ||
|-
| '''-1.0''' || '''34.1%''' || '''Struggling to land hits.'''
|-
| '''-2.0''' || '''23.3%''' ||
|-
| '''-3.0''' || '''15.9%''' ||
|}

===== 2. Damage Formulas =====
Damage is calculated as a percentage of the defender’s Max Health.

====== Army vs. Army ======
When an army hits another army, it '''deals roughly 10% of its Miltech in percentage of defender’s Max Health'''.

Base Damage: Miltech × 0.1 (±20%)

Variance: ±20% is the game simulating a damage range mechanic.

Critical Hit: Usually 1x. Increases to 3x if the attacker is at full health and the region is unoccupied (an "Ambush"), or by a small random chance based on the total number of armies in the fight.

====== Region vs. Army ======
Region defenses (fortifications/militia) '''fire every day at every hostile army'''. They deal less base damage but have much higher "Critical" lethality.

Base Damage: Region Miltech × 0.0225

The "Lethality" Multiplier: If an army is at full health and the region is unoccupied, the region can deal a massive 100x damage critical hit.

Overwhelmed Defenses: If more hostile armies are present than friendly armies, the region's damage output is reduced.

====== Occupying a Region (Army vs. Region) ======
When an army hits region defenses, it increases the Occupation %.

Base Damage: Army Miltech × 0.0225

Advantage Bonus: If your Army Miltech is higher than the region's base tech, you gain occupation faster.

Geography Modifiers: Occupation is slower in regions with huge populations (like Delhi) or massive land areas (like Siberia).

Crowding Penalty: Having too many armies in one spot (more than 1 per 100,000 km2) slows down occupation by up to 50%.

==== Combat Rules ====

Combat occurs whenever an army A is in a [[Regions|region]] R such that at least one of the following is true:
* A's home nation is [[Foreign_Relations#Wars|at war]] with the home nation of another army in R.
* R is partially or fully occupied and A's home nation owns R.
* R is partially or fully occupied and A's home nation is [[Foreign_Relations#Alliances|allies]] with the nation that owns R.
* A's home nation is [[Foreign_Relations#Wars|at war]] with the nation that owns R and R is not fully occupied.
* A's home nation does not exist and R is not fully occupied.
{{SpoilerBox|Alien-Related}}
* There is a [[Aliens#Megafauna|Megafauna Army]] in R that is not owned by the same faction that owns A.
* A's home nation is [[Foreign_Relations#Wars|at war]] with the nation that owns R and A is an [[Aliens#Invader_Armies|Invader Army]] and R is fully occupied by a war alliance that does not include the [[Aliens#Alien_Administration|Alien Nation]].
* A's home nation does not exist and A is an [[Aliens#Invader_Armies|Invader Army]] and R is fully occupied by a war alliance that does not include the [[Aliens#Alien_Administration|Alien Nation]].
* A is a [[Aliens#Megafauna|Megafauna Army]] that is owned by the {{icon|alien}}[[Aliens]] and R is not part of the [[Aliens#Alien_Administration|Alien Nation]] and R is not owned by a nation whose executive is controlled by a faction that has researched [[Xenofauna Harmony]].
* A is a [[Aliens#Megafauna|Megafauna Army]] that is owned by a faction F that is '''not''' the {{icon|alien}}[[Aliens]] and every non-[[Aliens#Megafauna|Megafauna]] army in R that is owned by F is owned by a nation that is [[Foreign_Relations#Wars|at war]] with the nation that owns R.
{{SpoilerBoxEnd}}

Combat is simulated as a daily exchange of attacks. For each army A:
# If there is an enemy army in the combat region, then A randomly selects one to fire at, preferring to avoid any armies owned by the same faction as A.
# If A is within a region that is hostile to A, then the region defenses fires at A.
# If A did not fire at anyone in the first step AND the region defenses missed its attack on A, then A fires at the region defenses.

Note that this means every army can fire at most one attack per day, but region defenses fire an attack on every hostile army every day.

Every attack has a hit chance that is determined by the gap between the attacker's {{TV|miltech}} and the defender's {{TV|miltech}}. But several modifiers may be applied to each side's {{TV|miltech}}, including but not limited to {{MissionIcon|Advise}}[[Advise|Advising]] [[Councilors]], {{icon|rugged}}rugged terrain bonuses, and damage taken.

When attacks hit, damage is taken, which scales based on the attacker's {{TV|miltech}}. When armies take damage, their health % drops. When region defenses take damage, their occupation % increases.

If a region is fully occupied it ceases fighting, but it can't change hands until the war is concluded. Regional economies and space facilities can take significant [[Regions#Region_Damage|collateral damage]] during fighting, although the rate of damage goes down as {{{TV|miltech}} goes up (representing more precise weaponry). Sufficient collateral damage will count as an [[Factions#Atrocity|atrocity]] by the army's owning faction.

==== Formulas ====

'''Miltech Calculations:'''

{| class="wikitable"
|-
! Factor !! Army Miltech A !! Army Miltech B !! Region Miltech
|-
| Base Miltech || Base Miltech || Base Miltech || Base Miltech
|-
| Councilor {{MissionIcon|Advise}}[[Advise]] Bonus || +0.01 per {{TVS|command}} || +0.01 per {{TVS|command}} || +0.01 per {{TVS|command}}
|-
| LEO Hab Bonus (capped at +0.3) || +0.03 per Military Lab || +0.03 per Military Lab || No Effect
|-
| In Home Nation || +0.2 || +0.2 || No Effect
|-
| In Home Nation AND region is {{icon|rugged}}rugged || +0.2 || +0.2 || +0.2
|-
| In Home Nation AND region is {{icon|core economic region|bgcolor=DarkSlateGray}}core economic || +0.1 || +0.1 || +0.1
|-
| Region is {{icon|rugged}}rugged and [[Mountain Warfare Doctrine]] is researched || +0.125 || +0.125 || +0.125
|-
| Region is {{icon|core economic region|bgcolor=DarkSlateGray}}core economic and [[Urban Warfare Doctrine]] is researched || +0.125 || +0.125 || +0.125
|-
| Army CP is disabled (Abandoned or {{MissionIcon|Crackdown}}[[Crackdown]]ed) || -0.2 || -0.2 || No Effect
|-
| In Allied (or Home) Nation || +0.05 per {{TV|cohesion}} of Allied Nation || No Effect || No Effect
|-
| Home Nation's {{TV|cohesion}} || No Effect || No Effect || +0.05 per {{TV|cohesion}}
|-
| Home Nation's {{TV|unrest}} || No Effect || No Effect || -0.05 per {{TV|unrest}}
|-
| Adjacent Regions belonging to Same Home Nation || No Effect || No Effect || +Fraction of such Regions that are unoccupied and not fighting × Home Nation's Miltech × 0.1 × (1 - 0.05 × Home Nation's {{TV|unrest}})
|-
| Remaining Combat Effectiveness || × (1 - 0.5 × Lost Health %) || × (1 - 0.5 × Lost Health %) || × (1 - 1/3 × Occupation %)
|-
|}

Note: If a nation has not completed the {{TV|found military}}, then its regions have effectively {{TV|miltech|0}} for combat.

'''Hit Chance Calculation:'''
* When an army fires at another army, the attacking army uses its '''Army Miltech A''' as the Attack value, while the defending army uses its '''Army Miltech B''' as the Defense value.
* When region defenses fire at an army, the region defenses use '''Region Miltech''' as the Attack value, while the defending army uses its '''Army Miltech A''' as the Defense value.
* When an army fires at the region defenses, the hit chance is always '''100%'''. (But the army only fires if the region defenses missed their attack.)

{| class="wikitable"
|-
! Condition
! Formula
|-
| Defense ≥ Attack
| <code>50% × 0.775^(1.5 × (Defense-Attack))</code>
|-
| Attack > Defense
| <code>100% − (50% × 0.775^(1.5 × (Attack-Defense)))</code>
|}

'''Damage taken:'''
When an army successfully lands a hit on another army, the defending army loses X% of its max health, where X calculated as follows:
# Set X to the attacking army's '''Army Miltech A'''.
# Multiply X by 0.1.
# Multiply X by a random value between 0.8 and 1.2.
# Multiply X by a critical multiplier Z, calculated as follows:
## Set Z to 1.
## Y% chance to set Z to 3, where Y is the square of the number of armies in the region that are involved in the war (allied armies that aren't part of the war don't count).
## If the attacking army is at full health and neither army is a [[Aliens#Megafauna|Megafauna]] and the region is 0% occupied, set Z to 3.
# All army damage bonuses from [[Technology|Projects]] are applied to X. (These bonuses are multiplicative and compounding, but often require the defending army to be a specific type of army.)

When the region defenses successfully land a hit on an army, the defending army loses X% of its max health, where X calculated as follows:
# Set X to the region's '''Region Miltech'''.
# Multiply X by 0.0225.
# Multiply X by a random value between 0.8 and 1.2.
# Let Y be the number of region-friendly armies in the region that are involved in the war (allied armies that aren't part of the war don't count) multiplied by the square of the number of region-hostile armies in the region.
# Multiply X by a critical multiplier Z, calculated as follows:
## Set Z to 1.
## Y% chance to set Z to 40.
## If the region is 0% occupied and the defending army is at full health, then set Z to 100.
## If Z is not 100, another Y% chance to set Z to 40.
## If Z is less than 40, (Y% / (100% - Y%)) chance to set Z to 5.
# All army damage bonuses from [[Technology|Projects]] are applied to X, except for bonuses against [[Aliens#Megafauna|Megafauna]]. (These bonuses are multiplicative and compounding, but often require the defending army to be a specific type of army.)
# Let H be the sum of the Remaining Combat Effectiveness multipliers of every region-hostile army in the region.
# Let F be the sum of the Remaining Combat Effectiveness multipliers of every region-friendly army in the region that is involved in the war (allied armies that aren't part of the war don't count).
# If H - F is more than 0, then multiply X by 1 - (H - F) / (H - F + 2).
# (1 - Region occupation % by defending army's home nation / H) chance to multiply X by 2.

If this last (1 - Region occupation % by defending army's home nation / H) chance fails, the region occupation % by the defending army's home nation actually '''decreases''' by D%, where D is calculated as follows:
# Set D to the region's Region Miltech.
# Multiply D by 0.0225.
# Multiply D by a random value between 0.8 and 1.2.
# Divide D by the number of region-hostile armies in the region.
# Multiply D by the '''Region Combat Action Multiplier''', which is calculated as 2 / (Region Population ^ 0.75 / Game Start Mean Average Region Population ^ 0.75 + Region Area ^ 0.5 / Median Region Area ^ 0.5).
# If D > 10, then set D to 10.

When an army hits the region defenses, the attacking army's home nation increases its occupation % of the region by X%, where X is calculated as follows:
# Set X to the attacking army's '''Army Miltech A'''.
# Let G be X - the defending region's home nation's base {{TV|miltech}} - the Councilor {{MissionIcon|Advise}}[[Advise]] Bonus for the defending region's home nation.
# If G > 0 then add G to X.
# Multiply X by 0.0225.
# Multiply X by a random value between 0.8 and 1.2.
# Multiply X by the '''Region Combat Action Multiplier''', which is calculated as 2 / (Region Population ^ 0.75 / Game Start Mean Average Region Population ^ 0.75 + Region Area ^ 0.5 / Median Region Area ^ 0.5).
# Multiply X by a critical multiplier Z, calculated as follows:
## Set Z to 1.
## Y% chance to set Z to 40.
## If the region is 0% occupied and the defending army is at full health, then set Z to 100.
## If Z is not 100, another Y% chance to set Z to 40.
## If Z is less than 40, (Y% / (100% - Y%)) chance to set Z to 5.
# Let C be the number of region-hostile armies in the region - the region area / 100000km².
# If C > 0, then multiply X by Max(1 - C * 0.02, 0.5)
# If X > 10, then set X to 10.

=== Army Operations ===
The faction that controls an army can conduct operations with it. They are:
{| class="wikitable"
! Operation !! width=85% | Effects
|-
| [[File:ICO DeployArmyOperation on.png|40px]] Deploy Army
| Move this Army to an adjacent region, including those of allies or wartime enemies. Armies will engage in battle with enemy armies and occupy enemy regions.
|-
| [[File:ICO DeployArmiesOperation on.png|40px]] Deploy Armies
| Move all stacked armies to an adjacent region, including those of allies or wartime enemies. Armies will engage in battle with enemy armies and occupy enemy regions.
|-
| [[File:ICO AssaultAlienAssetOperation on.png|40px]] Assault Alien Asset
| Launch an assault on a fixed alien target.
|-
| [[File:ICO AssaultSpaceFacilityOperation on.png|40px]] Assault Space Facility
| Destroy a fixed space facility in the region.
|-
| [[File:ICO RazeRegionOperation on.png|40px]] Raze Region
| Launch a general attack on economic and civilian targets in this region. Commits 5 to 25 [[Factions#Atrocity|atrocities]].
|-
| [[File:ICO ArmyGoHomeOperation on.png|40px]] Airlift Home
| Return this army to its home region during peacetime. Operation will not complete if home nation is at war.
|-
| [[File:ICO CancelArmyOperation on.png|40px]] Cancel Operation
| Cancel current operation for this Army. Army will resume fighting if enemies are present.
|}

'''Wiki Help wanted''': Look up the in-game image and description for the Army Annex Region operation and upload both here!

==== Annex Region ====

The game mechanics for army annex operations are explained here [[Foreign Relations#War_Annexation]].

==== Raze Region ====

See [[Regions#Region_Damage]].

==== Assault Alien Asset ====

{| class="wikitable"
|+ Damage Taken by {{TV|armies}} when they Assault Alien Assets
|-
! rowspan=2 | Mission Outcome !! colspan=2 | Type of Alien Asset
|-
! [[Aliens#Alien_Xenoforming|Xenoflora]] !! Other
|-
| Critical Failure || (30% to 150%) / Base {{TV|miltech}} || (150% to 300%) / Base {{TV|miltech}}
|-
| Normal Failure || (15% to 112.5%) / Base {{TV|miltech}} || (75% to 225%) / Base {{TV|miltech}}
|-
| Normal Success || (0% to 75%) / Base {{TV|miltech}} || (0% to 150%) / Base {{TV|miltech}}
|-
| Critical Success || (0% to 15%) / Base {{TV|miltech}} || (0% to 30%) / Base {{TV|miltech}}
|}

Note: Base {{TV|miltech}} is simply the army's home nation's {{TV|miltech}}, with all modifiers ignored.

See [[Aliens]] for spoilers on the different types of alien assets that can be assaulted, as well as the consequences of such assaults.

=== Army Healing ===

An injured human army will passively heal over time when all of the following conditions are true:
* It is in a friendly region<ref>A region owned by its home nation or a nation allied to its home nation</ref>.
* The region is currently not occupied or being occupied.
* It is not in battle with other armies.
* It is not currently performing an operation.

The % health that gets healed each day is calculated as follows:
# 0.5% Base.
# +0.5% more if the faction that controls the army also controls the [[Nations#Control_Point_Types|Defense Sector Control Point]] of the army's home nation.
# +0.5% more if the army is in its home nation.
# +0.5% more if the army is in its home region.
# Multiply the total by (1 - (Currently Healing Human Armies of Home Nation / (Total Human Armies of Home Nation + 1))).
#* Note: This step is currently bugged to never occur.
# +0.5% more if the faction that controls the army has researched the [[Rapid Repairing Materials]] project.
# +0.5% more if the faction that controls the army has researched the [[Predictive Logistics Systems]] project.

{{SpoilerBox|Alien-Related}}
Human armies that are owned by the {{icon|alien}}[[Aliens]] still follow the same healing rules.

But for the healing mechanics of Alien-related armies, see [[Aliens#Megafauna]] and [[Aliens#Invader_Armies]] instead.
{{SpoilerBoxEnd}}

<references />

=== Army Death ===

Whenever an army dies, multiple effects may occur:

==== Democracy Penalties ====

If the dead army belonged to a democratic human nation, then that nation suffers two penalties:
* A {{TV|cohesion}} loss equal to the nation's {{TV|democracy}} / 10.
* Applies [[Nations#Changing_Public_Opinion|Propaganda]] in the nation for the faction that owned the dead army. Propaganda strength is equal to (0 - the nation's {{TV|democracy}}).

==== Army IP Refund ====

Whenever a human army dies, its home [[Nations|nation]] receives a fraction of its {{TV|IP}} Cost as a refund. This refund is put directly into the {{TV|build army}} and/or {{TV|build navy}}, so it can often result in new {{TV|armies}} and/or {{TV|navies}} being built the next day. Specifically, the refund amounts are calculated as follows:

{| class="wikitable sortable" style="text-align:center;"
|+ Refund Amounts for {{TV|build army}}. Only applies if army did not die by nuke.
|-
! Army Died in Home Nation? !! Refund Amount
|-
| Yes || (30% to 50%) of {{TV|build army}} cost.
|-
| No || (15% to 25%) of {{TV|build army}} cost.
|}

{| class="wikitable sortable" style="text-align:center;"
|+ Refund Amounts for {{TV|build navy}}. Only applies if the dead army had a navy.
|-
! Army Died in Home Nation? !! Home Nation has [[Terrestrial_Warfare#Naval_Freedom|Naval Freedom]]? !! Army Died in Region that currently has [[Regions#World_Ocean_Access|World Ocean Access]]? !! Refund Amount
|-
| Yes || Yes || Yes || (70% to 90%) of {{TV|build navy}} cost.
|-
| Yes || Yes || No || (90% to 110%) of {{TV|build navy}} cost.
|-
| Yes || No || || (20% to 30%) of {{TV|build navy}} cost.
|-
| No || Yes || Yes || (60% to 80%) of {{TV|build navy}} cost.
|-
| No || Yes || No || (80% to 100%) of {{TV|build navy}} cost.
|-
| No || No || || (10% to 20%) of {{TV|build navy}} cost.
|}

==== Complete Milestones ====

If the army is related to the [[Aliens]] in any way, then the faction that kills it may achieve certain milestones from doing so. See [[Aliens]] for details.

==== Hate Vent ====

See [[Diplomacy#Alien_Hate_Vent]].

== Nuclear Warfare ==
Some nations have a number of {{TV|nukes}} available to them. These represent launching multiple strategic nuclear weapons at a target region. Launching nuclear strikes will devastate the economy of a [[Regions|region]] and the enemy {{TV|armies}} within it, although the damage will be somewhat mitigated if a nation is launching strikes on its own or an [[Foreign_Relations#Alliances|ally]]'s territory. Launching factions will be charged with committing one or more [[Factions#Atrocity|atrocities]]. Detonating a sufficient number of nuclear weapons may also have disastrous global effects. A region with {{icon|sto defense}}space defenses cannot be attacked with {{TV|nuke}}.

Nations can develop nuclear weapon with the {{TV|develop atomic bomb}}, which also gives {{TV|nuke|1}}. A nation with nuclear weapon program can build more with the {{TV|nuclear weapons}}.

Nations construct nuclear weapons as a deterrent to enemy invasion. Attempting to conquer a nuclear-armed nation will almost certainly lead to nuclear strikes in retaliation.

=== Valid Targets for a Nuclear Strike ===

Nukes can only be fired at [[Regions]]. The set of regions that a [[Nations|nation]] X can fire a nuke at is computed as follows:
# Add every region that is owned by any nation that is [[Foreign_Relations#Wars|at war]] with X.
# If X does not have a spaceflight program, then remove every region that is not adjacent to X and does not have [[Regions#World_Ocean_Access|ocean access]].
# If X does not have a spaceflight program and does not have [[Terrestrial_Warfare#Naval_Freedom|naval freedom]], then remove every region that is not adjacent to X.
# Add every region owned by X or an [[Foreign_Relations#Alliances|ally]] of X if the region currently contains an army that is owned by any nation that is [[Foreign_Relations#Wars|at war]] with X.
# For every region R, remove R unless one of the following is true:
#* R is owned by X.
#* R is owned by an [[Foreign_Relations#Alliances|ally]] of X.
#* R is owned by a nation that is [[Foreign_Relations#Wars|at war]] with X and R does not have a [[Nations#Space_Defenses|space defense facility]] built.

=== Effects of a Nuclear Strike ===

Launching nuclear weapons will do terrible and lasting damage to the targeted region, destroy any enemy {{TV|armies}} and all space facilities, and surely be seen with horror around the globe.

{| class="wikitable"
|+ Effects of a Nuclear Attack (In Chronological Order)
|-
! Category !! Amount for Offensive Nukes !! Amount for Defensive Nukes !! Modifiers
|-
| Target [[Nations#GDP_Per_Region|Region GDP]] || -52.5% to -87.5% || -15% to -25%
| rowspan=2 |
* [[Urban Armoring]] multiplies amount by 0.8.
* [[Civil Defense Programs]] multiplies amount by 0.8.
|-
| Target {{icon|pop}}[[Nations#Population|Region Population]] || -18.75% to -31.25% || -1.875% to -3.125%
|-
| Target Nation [[Nations#Sustainability|Pollution Multiplier]] || +0.075 to +0.125 || +0.00375 to +0.00625 || Multiplied by [[Nations#GDP_Per_Region|Region GDP]] / [[Nations#GDP|Nation GDP]]
|-
| Nuking Faction Commits [[Factions#Atrocity|Atrocities]] || colspan=2 | 1 per 100k {{TV|pop}} killed (rounded down).
|
* Multiply by 10 if nuke launcher is not on the defending side of any war where the target nation is on the attacking side.
** ...seems to apply for self-nukes too??
{{SpoilerBox|Alien-Related}}
** Does not apply if the target region is owned by the [[Aliens#Alien_Administration|Alien Nation]].
{{SpoilerBoxEnd}}
* Capped between 1 and 20.
|-
| All Human Nations' GDP || -25% × [[Nations#GDP_Per_Region|Region GDP]] / Global GDP + (0% to -2%) || -5% × [[Nations#GDP_Per_Region|Region GDP]] / Global GDP + (0% to -2%) || None
|-
| [[Family Ties]] Trait Effect || colspan=2 | {{TV|loyalty|-10}} || Multiply by 2 if Councilor's Faction launched the nuke.
|-
| Target Region is {{icon|core economic region|bgcolor=DarkSlateGray}}Core Economic || Remove {{icon|core economic region|bgcolor=DarkSlateGray}}Core Economic status || Nothing || None
|-
| All Human Nations' [[Nations#GDP|GDP]] || -2.5% + (0% to -2%) || N/A || If Target Region just lost {{icon|core economic region|bgcolor=DarkSlateGray}}Core Economic status.
|-
| Target Region is {{icon|oil region}}Core Oil or {{icon|resource region}}Core Mining || Remove {{icon|oil region}}Core Oil or {{icon|resource region}}Core Mining status || Nothing || None
|-
| All Human Nations' [[Nations#GDP|GDP]] || -1.5% + (0% to -2%) || N/A || If Target Region just lost {{icon|oil region}}Core Oil or {{icon|resource region}}Core Mining status.
|-
| Target Nation [[Nations#Priorities|Priorities]] || colspan=2| Set to 0 || Except {{icon|spoils}}Spoils, {{icon|unity}}Unity, and {{icon|oppression}}Oppression.
|-
| rowspan=2 | Destroy Space Assets in Target Region || colspan=2 | All {{icon|boost}}[[Nations#Boost|Boost]], {{icon|mc}}[[Nations#Mission_Control|Mission Control]] , and {{icon|sto defense|bgcolor=DarkSlateGray}}[[Nations#Space_Defenses|Space Defenses]] || If Target Nation is NOT Nuke Launcher
|-
| N/A || All {{icon|boost}}[[Nations#Boost|Boost]] and {{icon|sto defense|bgcolor=DarkSlateGray}}[[Nations#Space_Defenses|Space Defenses]], just 1 {{icon|mc}}[[Nations#Mission_Control|Mission Control]] || If Target Nation is Nuke Launcher
|-
| Target Nation {{icon|funding}}[[Nations#Funding|Funding]] || N/A || -50% × [[Nations#GDP_Per_Region|Region GDP]] / [[Nations#GDP|Nation GDP]] || If Target Nation is Nuke Launcher
|-
| rowspan=7 | Health of Each Army in Target Region || colspan=2 | Instant Death || For the Strongest<ref>The strongest army is the army whose health % × Base {{TV|miltech}} is the highest.</ref> Army that is not Ally of Nuker<ref name=allyofnuker>An army is an ally of the nuker if any of the following are true:
* The army is owned by the nuking nation.
* The army is owned by an ally of the nuking nation.
* The army is owned by the nuking faction and not a [[Aliens#Megafauna|Megafauna]].</ref>.
|-
| colspan=2 | Min(0%, (-100% + (1% to 5%) × (Base {{icon|miltech}}MilTech - 3.79)) × 0.140625) || For each [[Aliens#Invader Armies|Alien Invader Army]] that is not Ally of Nuker<ref name=allyofnuker />.
|-
| colspan=2 | Min(0%, -100% + (1% to 5%) × Max(0, Base {{icon|miltech}}MilTech - 3.79) × 0.75 if [[Army Nuclear Hardening]] researched × 0.140625 if working for Aliens) || 50% chance for each Human army that is not Ally of Nuker<ref name=allyofnuker />.
|-
| colspan=2 | -100% × 0.75 if [[Army Nuclear Hardening]] researched × 0.140625 if working for Aliens || The other 50% chance for each Human army that is not Ally of Nuker<ref name=allyofnuker />.
|-
| colspan=2 | Min(0%, -100% + (1% to 5%) × Max(0, Base {{icon|miltech}}MilTech - 3.79)) || 50% chance for each Megafauna army.
|-
| colspan=2 | -100% || The other 50% chance for each [[Aliens#Megafauna|Megafauna]] army.
|-
| colspan=2 | -100% / (48 to 52) || For each army that is Ally of Nuker<ref name=allyofnuker />.
|-
| Each [[Councilors|Councilor]] in Target Region || colspan=2 | 50% Chance to die || [[Survivor]] trait gives immunity.
|-
| [[Aliens#Xenoforming|Alien Xenoforming]] || colspan=2 | Set to 0 Xenoflora Growth Levels || None
|-
| Add [[Climate Change|Aerosols]] || colspan=2 | 0.00777 || Multiply by Region Area (km²) / 10000km² if Region is an Island smaller than 10000km².
|-
| colspan=4 | Target Region Gains 1 Layer of Nuclear Fallout
|}

<references />

== Orbital Bombardment ==

[[Spaceships]] with certain weapon modules can bombard hostile armies from orbit.

See [[Fleets#Orbital_Bombardment]] for more details.

{{Mechanics_Navbox}}

Terrestrial Warfare

2026-03-17T19:39:30Z

76561197989421583: Correction of a mistake '==='

This page mainly discusses the mechanics for fighting terrestrial wars. For a more detailed discussion about starting and ending wars, see [[Foreign Relations#Wars]] instead.

[[Foreign Relations#Wars|Wars]] begin when a [[Councilors|councilor]] for the executive [[Factions|faction]] of one of two [[Foreign Relations#Rivals|Rivals]] selects the [[Foreign Relations#Declaring_Wars|War policy]] against the rival. All war-capable [[Foreign Relations#Alliances|allies]] of the defending rival (with an army or nuclear weapons) join the war. All war-capable allies of the attacker are given the option to join on the attacker's side.

To win a war, an [[Nations#Armies|army]] must occupy the enemy's {{icon|capital|bgcolor=DarkSlateGray}}Capital [[Regions|region]]. At that moment, the war ends, triggering a [[Foreign Relations#War_Conquest|regime change]]. [[Foreign Relations#Claims|Claimed regions]] change hands to the occupier and its allies. If any of the invaded nation remains, its control point owners are replaced with those of the victor. Some of the nation's stats change when a new regime is installed, sometimes in unpredictable ways, but the new ruling faction will be able to fund [[Nations#Direct_Investment|Direct Investments]] into the nation at greatly reduced {{TV|influence}} cost for a period of one year. Unoccupied [[Regions]] and surviving enemy armies will contribute to greater {{TV|unrest}} following a regime change.

Wars may also end with a [[Foreign Relations#Seeking_Peace|simple peace]] where both sides return to the prewar status quo.

== Armies ==

[[Nations#Armies|Armies]] represent multiple modern divisions that are capable of gaining and holding territory in other [[Nations]]. Control of an army is gained after councilors gain at least partial control of a nation. Most [[Nations]] don't have armies at the campaign start, but [[Nations]] with sufficient {{TV|pop}} can build new ones with enough investment into the {{TV|build army}}. While powerful, armies are a drag on a nation's {{icon|ip|bgcolor=DarkSlateGray}}economic development and remain subject to the international relations of their home countries, which too can be managed with sufficient control of a nation.

Armies have a [[File:ICO army HQ.png|20px]]headquarters region in their home nation. If located there, they incur a smaller cost to the nation's {{icon|ip|bgcolor=DarkSlateGray}}economic development.

Armies rely on two key values: its parent nation's {{TV|miltech}} level and its strength. The strength value measures how much damage the army has taken. Armies usually passively and freely repair themselves when not fighting in a friendly region.

Some armies have a {{icon|navy}}[[Nations#Navies|Navy]] upgrade that allows them to transit oceans. During wartime, a nation's navies can only cross the water if the nation has naval superiority over its foes. Only larger or wealthier [[Nations]] have the capability to {{icon|build navy}}build and project power with {{icon|navy}}navies.

=== Naval Freedom ===

For each [[Foreign Relations#Wars|war]], the game computes for each side the sum of the {{TV|miltech}} of the armies that have a navy upgrade. If one side has a higher sum than the other, then the other side of the war is blockaded: all of its nations no longer have Naval Freedom.

As a result, a nation only has Naval Freedom if it is not blockaded in any of the wars that it is involved in.

Notably, since wars can get very messy, with multiple overlapping wars, it is actually entirely possible for all nations to lose their Naval Freedom.

Consider a simple example with 3 nations: A, B, and C, such that:
* A has a single navy with {{TV|miltech|3}}.
* B has a single navy with {{TV|miltech|2}}.
* C has a single navy with {{TV|miltech|2}}.

Suppose there are three overlapping wars X, Y, and Z, such that:
* War X pits A against B.
* War Y pits A against C.
* War Z pits A against B and C.

Then the result would be:
* War X blockades B, since A's 3 naval score beats B's 2 naval score.
* War Y blockades C, since A's 3 naval score beats C's 2 naval score.
* War Z blockades A, since A's 3 naval score is beaten by the combined naval score of B's 2 naval score added to C's 2 naval score = 4 naval score.

So all 3 nations have no Naval Freedom.

=== Army Movement ===

Armies are allowed to be in any region R such that one of the following is true:
* R belongs to the army's home nation.
* R belongs to a nation that is [[Foreign Relations#Alliances|allied]] to the army's home nation.
* R belongs to a nation that is [[Foreign Relations#Wars|at war]] with the army's home nation.

An army can directly travel from any region R1 to any region R2 such that at least one of the following is true:
* R1 and R2 are adjacent.<ref name=adjacent>Note: Certain research projects can make pairs of regions become adjacent.</ref>
* R1 and R2 are adjacent only for friendly armies<ref name=adjacent />, and both R1 and R2 belong to nation(s) that are not at war with the army's home nation.
* All of the following are true:
** R1 and R2 both currently have [[Regions#World_Ocean_Access|world ocean access]].
** The army's home nation has [[Terrestrial_Warfare#Naval_Freedom|naval freedom]].
** Either the army does not need to travel between the Black Sea and the World Ocean, or the army's home nation has access to the Turkish Strait.

A nation has Turkish Strait access as long as one of the following is true:
* It is not at war with the nation that owns the Istanbul region.
* The Istanbul region is fully occupied.

<references />

==== Land Movement ====

The time needed for an army to travel directly between two adjacent regions without using a navy is calculated as follows:
<pre> Duration (days) = Distance (km) / 300 (km/day) * 4 / Miltech </pre>

But this value is affected by the following multipliers:
{| class="wikitable sortable" style="text-align:center;"
|-
! rowspan=2| Condition(s) !! colspan=3|Multiplier Value When:
|-
! Only Origin Region is Small<ref name=small>A region is small if it is smaller than 150000km².</ref> !! Only Destination Region is Small<ref name=small />!! Otherwise
|-
| Origin Region is not friendly OR Origin Region has enemy armies || 5 ^ 0.2 || 5 ^ 0.8 || 5 ^ 0.5
|-
| (Origin Region is not friendly OR Origin Region has enemy armies) AND Origin Region is {{icon|rugged}}Rugged || 1.5 ^ 0.2 || 1.5 ^ 0.8 || 1.5 ^ 0.5
|-
| Origin Region is friendly AND Origin Region has no enemy armies AND Origin Region is {{icon|rugged}}Rugged || 1.25 ^ 0.2 || 1.25 ^ 0.8 || 1.25 ^ 0.5
|-
| Origin Region is friendly AND Origin Region has no enemy armies AND Origin Nation has {{TV|unrest|>5}} || (1 + (Origin Nation {{TV|unrest}} - 5) / 6.5) ^ 0.2 || (1 + (Origin Nation {{TV|unrest}} - 5) / 6.5) ^ 0.8 || (1 + (Origin Nation {{TV|unrest}} - 5) / 6.5) ^ 0.5
|-
| Origin Region is a {{icon|colony|bgcolor=DarkSlateGray}}Colony || 1.5 ^ 0.2 || 1.5 ^ 0.8 || 1.5 ^ 0.5
|-
| Destination Region is not friendly || 5 ^ 0.8 || 5 ^ 0.2 || 5 ^ 0.5
|-
| Destination Region is not friendly AND Destination Region is {{icon|rugged}}Rugged || 1.5 ^ 0.8 || 1.5 ^ 0.2 || 1.5 ^ 0.5
|-
| Destination Region is friendly AND Destination Region is {{icon|rugged}}Rugged || 1.25 ^ 0.8 || 1.25 ^ 0.2 || 1.25 ^ 0.5
|-
| Destination Region is friendly AND Destination Nation has {{TV|unrest|>5}} || (1 + (Destination Nation {{TV|unrest}} - 5) / 6.5) ^ 0.8 || (1 + (Destination Nation {{TV|unrest}} - 5) / 6.5) ^ 0.2 || (1 + (Destination Nation {{TV|unrest}} - 5) / 6.5) ^ 0.5
|-
| Destination Region is a {{icon|colony|bgcolor=DarkSlateGray}}Colony || 1.5 ^ 0.8 || 1.5 ^ 0.2 || 1.5 ^ 0.5
|}

<references />

==== Naval Movement ====

The time needed for an army to travel between two regions without using a navy is calculated as follows:
<pre> Duration (days) = (14 days + Distance (km) / 792 (km/day) ) * 4 / Miltech </pre>

But this value is affected by a number of complex calculations that consider the different possible sea routes. In particular, the duration can be significantly affected by whether the army's nation has access to the Suez and Panama canals.

A nation has canal access as long as one of the following is true:
* It is not at war with the nation that owns the Canal region.
* The Canal region is fully occupied.

The Canal regions are:
* Cairo for the Suez Canal.
* Panama City for the Panama Canal.

=== Army Battle ===

==== Simplified Combat Rules ====

Combat in ''Terra Invicta'' is a comparison of Miltech levels. Higher Miltech means you hit more often and deal more damage. If two forces have equal Miltech, the base hit chance is 50%.

===== 1. Hit Chance (The Accuracy Gap) =====
The game calculates the difference (Δ) between the Attacker's Miltech and the Defender's Miltech.

If Miltechs are equal: 50% Hit Chance.
If you have the advantage: Your hit chance climbs toward 100%.
If you are outclassed: Your hit chance drops toward 0%.

Hit Chance (Advantage)=100%−(50%×0.7751.5×Δ)
Hit Chance (Disadvantage)=50%×0.7751.5×Δ

'''Quick Guide:''' A 1-point Miltech advantage raises your hit chance to roughly 66%. A 2-point advantage raises it to roughly 79%.
====== Hit Chance Reference Table ======

The following table shows the 1vs1 hit chance based on the Miltech difference (Delta = Attacker Miltech - Defender Miltech).

{| class="wikitable" style="text-align: center;"
|-
! Miltech Difference (Delta) !! Hit Chance !! Note
|-
| '''+3.0''' || '''84.1%''' ||
|-
| '''+2.0''' || '''76.7%''' ||
|-
| '''+1.0''' || '''65.9%''' || '''Strong offensive edge.'''
|-
| +0.8 || 63.2% ||
|-
| +0.6 || 60.3% ||
|-
| +0.4 || 57.1% ||
|-
| +0.2 || 53.7% ||
|-
| '''0.0''' || '''50.0%''' || '''Even match; coin-flip odds.'''
|-
| -0.2 || 46.3% ||
|-
| -0.4 || 42.9% ||
|-
| -0.6 || 39.7% ||
|-
| -0.8 || 36.8% ||
|-
| '''-1.0''' || '''34.1%''' || '''Struggling to land hits.'''
|-
| '''-2.0''' || '''23.3%''' ||
|-
| '''-3.0''' || '''15.9%''' ||
|}

===== 2. Damage Formulas =====
Damage is calculated as a percentage of the defender’s Max Health.

====== Army vs. Army ======
When an army hits another army, it '''deals roughly 10% of its Miltech in percentage of defender’s Max Health'''.

Base Damage: Miltech × 0.1 (±20%)

Variance: ±20% is the game simulating a damage range mechanic.

Critical Hit: Usually 1x. Increases to 3x if the attacker is at full health and the region is unoccupied (an "Ambush"), or by a small random chance based on the total number of armies in the fight.

====== Region vs. Army ======
Region defenses (fortifications/militia) fire every day at every hostile army. They deal less base damage but have much higher "Critical" lethality.

Base Damage: Region Miltech × 0.0225

The "Lethality" Multiplier: If an army is at full health and the region is unoccupied, the region can deal a massive 100x damage critical hit.

Overwhelmed Defenses: If more hostile armies are present than friendly armies, the region's damage output is reduced.

====== Occupying a Region (Army vs. Region) ======
When an army hits region defenses, it increases the Occupation %.

Base Damage: Army Miltech × 0.0225

Advantage Bonus: If your Army Miltech is higher than the region's base tech, you gain occupation faster.

Geography Modifiers: Occupation is slower in regions with huge populations (like Delhi) or massive land areas (like Siberia).

Crowding Penalty: Having too many armies in one spot (more than 1 per 100,000 km2) slows down occupation by up to 50%.

==== Combat Rules ====

Combat occurs whenever an army A is in a [[Regions|region]] R such that at least one of the following is true:
* A's home nation is [[Foreign_Relations#Wars|at war]] with the home nation of another army in R.
* R is partially or fully occupied and A's home nation owns R.
* R is partially or fully occupied and A's home nation is [[Foreign_Relations#Alliances|allies]] with the nation that owns R.
* A's home nation is [[Foreign_Relations#Wars|at war]] with the nation that owns R and R is not fully occupied.
* A's home nation does not exist and R is not fully occupied.
{{SpoilerBox|Alien-Related}}
* There is a [[Aliens#Megafauna|Megafauna Army]] in R that is not owned by the same faction that owns A.
* A's home nation is [[Foreign_Relations#Wars|at war]] with the nation that owns R and A is an [[Aliens#Invader_Armies|Invader Army]] and R is fully occupied by a war alliance that does not include the [[Aliens#Alien_Administration|Alien Nation]].
* A's home nation does not exist and A is an [[Aliens#Invader_Armies|Invader Army]] and R is fully occupied by a war alliance that does not include the [[Aliens#Alien_Administration|Alien Nation]].
* A is a [[Aliens#Megafauna|Megafauna Army]] that is owned by the {{icon|alien}}[[Aliens]] and R is not part of the [[Aliens#Alien_Administration|Alien Nation]] and R is not owned by a nation whose executive is controlled by a faction that has researched [[Xenofauna Harmony]].
* A is a [[Aliens#Megafauna|Megafauna Army]] that is owned by a faction F that is '''not''' the {{icon|alien}}[[Aliens]] and every non-[[Aliens#Megafauna|Megafauna]] army in R that is owned by F is owned by a nation that is [[Foreign_Relations#Wars|at war]] with the nation that owns R.
{{SpoilerBoxEnd}}

Combat is simulated as a daily exchange of attacks. For each army A:
# If there is an enemy army in the combat region, then A randomly selects one to fire at, preferring to avoid any armies owned by the same faction as A.
# If A is within a region that is hostile to A, then the region defenses fires at A.
# If A did not fire at anyone in the first step AND the region defenses missed its attack on A, then A fires at the region defenses.

Note that this means every army can fire at most one attack per day, but region defenses fire an attack on every hostile army every day.

Every attack has a hit chance that is determined by the gap between the attacker's {{TV|miltech}} and the defender's {{TV|miltech}}. But several modifiers may be applied to each side's {{TV|miltech}}, including but not limited to {{MissionIcon|Advise}}[[Advise|Advising]] [[Councilors]], {{icon|rugged}}rugged terrain bonuses, and damage taken.

When attacks hit, damage is taken, which scales based on the attacker's {{TV|miltech}}. When armies take damage, their health % drops. When region defenses take damage, their occupation % increases.

If a region is fully occupied it ceases fighting, but it can't change hands until the war is concluded. Regional economies and space facilities can take significant [[Regions#Region_Damage|collateral damage]] during fighting, although the rate of damage goes down as {{{TV|miltech}} goes up (representing more precise weaponry). Sufficient collateral damage will count as an [[Factions#Atrocity|atrocity]] by the army's owning faction.

==== Formulas ====

'''Miltech Calculations:'''

{| class="wikitable"
|-
! Factor !! Army Miltech A !! Army Miltech B !! Region Miltech
|-
| Base Miltech || Base Miltech || Base Miltech || Base Miltech
|-
| Councilor {{MissionIcon|Advise}}[[Advise]] Bonus || +0.01 per {{TVS|command}} || +0.01 per {{TVS|command}} || +0.01 per {{TVS|command}}
|-
| LEO Hab Bonus (capped at +0.3) || +0.03 per Military Lab || +0.03 per Military Lab || No Effect
|-
| In Home Nation || +0.2 || +0.2 || No Effect
|-
| In Home Nation AND region is {{icon|rugged}}rugged || +0.2 || +0.2 || +0.2
|-
| In Home Nation AND region is {{icon|core economic region|bgcolor=DarkSlateGray}}core economic || +0.1 || +0.1 || +0.1
|-
| Region is {{icon|rugged}}rugged and [[Mountain Warfare Doctrine]] is researched || +0.125 || +0.125 || +0.125
|-
| Region is {{icon|core economic region|bgcolor=DarkSlateGray}}core economic and [[Urban Warfare Doctrine]] is researched || +0.125 || +0.125 || +0.125
|-
| Army CP is disabled (Abandoned or {{MissionIcon|Crackdown}}[[Crackdown]]ed) || -0.2 || -0.2 || No Effect
|-
| In Allied (or Home) Nation || +0.05 per {{TV|cohesion}} of Allied Nation || No Effect || No Effect
|-
| Home Nation's {{TV|cohesion}} || No Effect || No Effect || +0.05 per {{TV|cohesion}}
|-
| Home Nation's {{TV|unrest}} || No Effect || No Effect || -0.05 per {{TV|unrest}}
|-
| Adjacent Regions belonging to Same Home Nation || No Effect || No Effect || +Fraction of such Regions that are unoccupied and not fighting × Home Nation's Miltech × 0.1 × (1 - 0.05 × Home Nation's {{TV|unrest}})
|-
| Remaining Combat Effectiveness || × (1 - 0.5 × Lost Health %) || × (1 - 0.5 × Lost Health %) || × (1 - 1/3 × Occupation %)
|-
|}

Note: If a nation has not completed the {{TV|found military}}, then its regions have effectively {{TV|miltech|0}} for combat.

'''Hit Chance Calculation:'''
* When an army fires at another army, the attacking army uses its '''Army Miltech A''' as the Attack value, while the defending army uses its '''Army Miltech B''' as the Defense value.
* When region defenses fire at an army, the region defenses use '''Region Miltech''' as the Attack value, while the defending army uses its '''Army Miltech A''' as the Defense value.
* When an army fires at the region defenses, the hit chance is always '''100%'''. (But the army only fires if the region defenses missed their attack.)

{| class="wikitable"
|-
! Condition
! Formula
|-
| Defense ≥ Attack
| <code>50% × 0.775^(1.5 × (Defense-Attack))</code>
|-
| Attack > Defense
| <code>100% − (50% × 0.775^(1.5 × (Attack-Defense)))</code>
|}

'''Damage taken:'''
When an army successfully lands a hit on another army, the defending army loses X% of its max health, where X calculated as follows:
# Set X to the attacking army's '''Army Miltech A'''.
# Multiply X by 0.1.
# Multiply X by a random value between 0.8 and 1.2.
# Multiply X by a critical multiplier Z, calculated as follows:
## Set Z to 1.
## Y% chance to set Z to 3, where Y is the square of the number of armies in the region that are involved in the war (allied armies that aren't part of the war don't count).
## If the attacking army is at full health and neither army is a [[Aliens#Megafauna|Megafauna]] and the region is 0% occupied, set Z to 3.
# All army damage bonuses from [[Technology|Projects]] are applied to X. (These bonuses are multiplicative and compounding, but often require the defending army to be a specific type of army.)

When the region defenses successfully land a hit on an army, the defending army loses X% of its max health, where X calculated as follows:
# Set X to the region's '''Region Miltech'''.
# Multiply X by 0.0225.
# Multiply X by a random value between 0.8 and 1.2.
# Let Y be the number of region-friendly armies in the region that are involved in the war (allied armies that aren't part of the war don't count) multiplied by the square of the number of region-hostile armies in the region.
# Multiply X by a critical multiplier Z, calculated as follows:
## Set Z to 1.
## Y% chance to set Z to 40.
## If the region is 0% occupied and the defending army is at full health, then set Z to 100.
## If Z is not 100, another Y% chance to set Z to 40.
## If Z is less than 40, (Y% / (100% - Y%)) chance to set Z to 5.
# All army damage bonuses from [[Technology|Projects]] are applied to X, except for bonuses against [[Aliens#Megafauna|Megafauna]]. (These bonuses are multiplicative and compounding, but often require the defending army to be a specific type of army.)
# Let H be the sum of the Remaining Combat Effectiveness multipliers of every region-hostile army in the region.
# Let F be the sum of the Remaining Combat Effectiveness multipliers of every region-friendly army in the region that is involved in the war (allied armies that aren't part of the war don't count).
# If H - F is more than 0, then multiply X by 1 - (H - F) / (H - F + 2).
# (1 - Region occupation % by defending army's home nation / H) chance to multiply X by 2.

If this last (1 - Region occupation % by defending army's home nation / H) chance fails, the region occupation % by the defending army's home nation actually '''decreases''' by D%, where D is calculated as follows:
# Set D to the region's Region Miltech.
# Multiply D by 0.0225.
# Multiply D by a random value between 0.8 and 1.2.
# Divide D by the number of region-hostile armies in the region.
# Multiply D by the '''Region Combat Action Multiplier''', which is calculated as 2 / (Region Population ^ 0.75 / Game Start Mean Average Region Population ^ 0.75 + Region Area ^ 0.5 / Median Region Area ^ 0.5).
# If D > 10, then set D to 10.

When an army hits the region defenses, the attacking army's home nation increases its occupation % of the region by X%, where X is calculated as follows:
# Set X to the attacking army's '''Army Miltech A'''.
# Let G be X - the defending region's home nation's base {{TV|miltech}} - the Councilor {{MissionIcon|Advise}}[[Advise]] Bonus for the defending region's home nation.
# If G > 0 then add G to X.
# Multiply X by 0.0225.
# Multiply X by a random value between 0.8 and 1.2.
# Multiply X by the '''Region Combat Action Multiplier''', which is calculated as 2 / (Region Population ^ 0.75 / Game Start Mean Average Region Population ^ 0.75 + Region Area ^ 0.5 / Median Region Area ^ 0.5).
# Multiply X by a critical multiplier Z, calculated as follows:
## Set Z to 1.
## Y% chance to set Z to 40.
## If the region is 0% occupied and the defending army is at full health, then set Z to 100.
## If Z is not 100, another Y% chance to set Z to 40.
## If Z is less than 40, (Y% / (100% - Y%)) chance to set Z to 5.
# Let C be the number of region-hostile armies in the region - the region area / 100000km².
# If C > 0, then multiply X by Max(1 - C * 0.02, 0.5)
# If X > 10, then set X to 10.

=== Army Operations ===
The faction that controls an army can conduct operations with it. They are:
{| class="wikitable"
! Operation !! width=85% | Effects
|-
| [[File:ICO DeployArmyOperation on.png|40px]] Deploy Army
| Move this Army to an adjacent region, including those of allies or wartime enemies. Armies will engage in battle with enemy armies and occupy enemy regions.
|-
| [[File:ICO DeployArmiesOperation on.png|40px]] Deploy Armies
| Move all stacked armies to an adjacent region, including those of allies or wartime enemies. Armies will engage in battle with enemy armies and occupy enemy regions.
|-
| [[File:ICO AssaultAlienAssetOperation on.png|40px]] Assault Alien Asset
| Launch an assault on a fixed alien target.
|-
| [[File:ICO AssaultSpaceFacilityOperation on.png|40px]] Assault Space Facility
| Destroy a fixed space facility in the region.
|-
| [[File:ICO RazeRegionOperation on.png|40px]] Raze Region
| Launch a general attack on economic and civilian targets in this region. Commits 5 to 25 [[Factions#Atrocity|atrocities]].
|-
| [[File:ICO ArmyGoHomeOperation on.png|40px]] Airlift Home
| Return this army to its home region during peacetime. Operation will not complete if home nation is at war.
|-
| [[File:ICO CancelArmyOperation on.png|40px]] Cancel Operation
| Cancel current operation for this Army. Army will resume fighting if enemies are present.
|}

'''Wiki Help wanted''': Look up the in-game image and description for the Army Annex Region operation and upload both here!

==== Annex Region ====

The game mechanics for army annex operations are explained here [[Foreign Relations#War_Annexation]].

==== Raze Region ====

See [[Regions#Region_Damage]].

==== Assault Alien Asset ====

{| class="wikitable"
|+ Damage Taken by {{TV|armies}} when they Assault Alien Assets
|-
! rowspan=2 | Mission Outcome !! colspan=2 | Type of Alien Asset
|-
! [[Aliens#Alien_Xenoforming|Xenoflora]] !! Other
|-
| Critical Failure || (30% to 150%) / Base {{TV|miltech}} || (150% to 300%) / Base {{TV|miltech}}
|-
| Normal Failure || (15% to 112.5%) / Base {{TV|miltech}} || (75% to 225%) / Base {{TV|miltech}}
|-
| Normal Success || (0% to 75%) / Base {{TV|miltech}} || (0% to 150%) / Base {{TV|miltech}}
|-
| Critical Success || (0% to 15%) / Base {{TV|miltech}} || (0% to 30%) / Base {{TV|miltech}}
|}

Note: Base {{TV|miltech}} is simply the army's home nation's {{TV|miltech}}, with all modifiers ignored.

See [[Aliens]] for spoilers on the different types of alien assets that can be assaulted, as well as the consequences of such assaults.

=== Army Healing ===

An injured human army will passively heal over time when all of the following conditions are true:
* It is in a friendly region<ref>A region owned by its home nation or a nation allied to its home nation</ref>.
* The region is currently not occupied or being occupied.
* It is not in battle with other armies.
* It is not currently performing an operation.

The % health that gets healed each day is calculated as follows:
# 0.5% Base.
# +0.5% more if the faction that controls the army also controls the [[Nations#Control_Point_Types|Defense Sector Control Point]] of the army's home nation.
# +0.5% more if the army is in its home nation.
# +0.5% more if the army is in its home region.
# Multiply the total by (1 - (Currently Healing Human Armies of Home Nation / (Total Human Armies of Home Nation + 1))).
#* Note: This step is currently bugged to never occur.
# +0.5% more if the faction that controls the army has researched the [[Rapid Repairing Materials]] project.
# +0.5% more if the faction that controls the army has researched the [[Predictive Logistics Systems]] project.

{{SpoilerBox|Alien-Related}}
Human armies that are owned by the {{icon|alien}}[[Aliens]] still follow the same healing rules.

But for the healing mechanics of Alien-related armies, see [[Aliens#Megafauna]] and [[Aliens#Invader_Armies]] instead.
{{SpoilerBoxEnd}}

<references />

=== Army Death ===

Whenever an army dies, multiple effects may occur:

==== Democracy Penalties ====

If the dead army belonged to a democratic human nation, then that nation suffers two penalties:
* A {{TV|cohesion}} loss equal to the nation's {{TV|democracy}} / 10.
* Applies [[Nations#Changing_Public_Opinion|Propaganda]] in the nation for the faction that owned the dead army. Propaganda strength is equal to (0 - the nation's {{TV|democracy}}).

==== Army IP Refund ====

Whenever a human army dies, its home [[Nations|nation]] receives a fraction of its {{TV|IP}} Cost as a refund. This refund is put directly into the {{TV|build army}} and/or {{TV|build navy}}, so it can often result in new {{TV|armies}} and/or {{TV|navies}} being built the next day. Specifically, the refund amounts are calculated as follows:

{| class="wikitable sortable" style="text-align:center;"
|+ Refund Amounts for {{TV|build army}}. Only applies if army did not die by nuke.
|-
! Army Died in Home Nation? !! Refund Amount
|-
| Yes || (30% to 50%) of {{TV|build army}} cost.
|-
| No || (15% to 25%) of {{TV|build army}} cost.
|}

{| class="wikitable sortable" style="text-align:center;"
|+ Refund Amounts for {{TV|build navy}}. Only applies if the dead army had a navy.
|-
! Army Died in Home Nation? !! Home Nation has [[Terrestrial_Warfare#Naval_Freedom|Naval Freedom]]? !! Army Died in Region that currently has [[Regions#World_Ocean_Access|World Ocean Access]]? !! Refund Amount
|-
| Yes || Yes || Yes || (70% to 90%) of {{TV|build navy}} cost.
|-
| Yes || Yes || No || (90% to 110%) of {{TV|build navy}} cost.
|-
| Yes || No || || (20% to 30%) of {{TV|build navy}} cost.
|-
| No || Yes || Yes || (60% to 80%) of {{TV|build navy}} cost.
|-
| No || Yes || No || (80% to 100%) of {{TV|build navy}} cost.
|-
| No || No || || (10% to 20%) of {{TV|build navy}} cost.
|}

==== Complete Milestones ====

If the army is related to the [[Aliens]] in any way, then the faction that kills it may achieve certain milestones from doing so. See [[Aliens]] for details.

==== Hate Vent ====

See [[Diplomacy#Alien_Hate_Vent]].

== Nuclear Warfare ==
Some nations have a number of {{TV|nukes}} available to them. These represent launching multiple strategic nuclear weapons at a target region. Launching nuclear strikes will devastate the economy of a [[Regions|region]] and the enemy {{TV|armies}} within it, although the damage will be somewhat mitigated if a nation is launching strikes on its own or an [[Foreign_Relations#Alliances|ally]]'s territory. Launching factions will be charged with committing one or more [[Factions#Atrocity|atrocities]]. Detonating a sufficient number of nuclear weapons may also have disastrous global effects. A region with {{icon|sto defense}}space defenses cannot be attacked with {{TV|nuke}}.

Nations can develop nuclear weapon with the {{TV|develop atomic bomb}}, which also gives {{TV|nuke|1}}. A nation with nuclear weapon program can build more with the {{TV|nuclear weapons}}.

Nations construct nuclear weapons as a deterrent to enemy invasion. Attempting to conquer a nuclear-armed nation will almost certainly lead to nuclear strikes in retaliation.

=== Valid Targets for a Nuclear Strike ===

Nukes can only be fired at [[Regions]]. The set of regions that a [[Nations|nation]] X can fire a nuke at is computed as follows:
# Add every region that is owned by any nation that is [[Foreign_Relations#Wars|at war]] with X.
# If X does not have a spaceflight program, then remove every region that is not adjacent to X and does not have [[Regions#World_Ocean_Access|ocean access]].
# If X does not have a spaceflight program and does not have [[Terrestrial_Warfare#Naval_Freedom|naval freedom]], then remove every region that is not adjacent to X.
# Add every region owned by X or an [[Foreign_Relations#Alliances|ally]] of X if the region currently contains an army that is owned by any nation that is [[Foreign_Relations#Wars|at war]] with X.
# For every region R, remove R unless one of the following is true:
#* R is owned by X.
#* R is owned by an [[Foreign_Relations#Alliances|ally]] of X.
#* R is owned by a nation that is [[Foreign_Relations#Wars|at war]] with X and R does not have a [[Nations#Space_Defenses|space defense facility]] built.

=== Effects of a Nuclear Strike ===

Launching nuclear weapons will do terrible and lasting damage to the targeted region, destroy any enemy {{TV|armies}} and all space facilities, and surely be seen with horror around the globe.

{| class="wikitable"
|+ Effects of a Nuclear Attack (In Chronological Order)
|-
! Category !! Amount for Offensive Nukes !! Amount for Defensive Nukes !! Modifiers
|-
| Target [[Nations#GDP_Per_Region|Region GDP]] || -52.5% to -87.5% || -15% to -25%
| rowspan=2 |
* [[Urban Armoring]] multiplies amount by 0.8.
* [[Civil Defense Programs]] multiplies amount by 0.8.
|-
| Target {{icon|pop}}[[Nations#Population|Region Population]] || -18.75% to -31.25% || -1.875% to -3.125%
|-
| Target Nation [[Nations#Sustainability|Pollution Multiplier]] || +0.075 to +0.125 || +0.00375 to +0.00625 || Multiplied by [[Nations#GDP_Per_Region|Region GDP]] / [[Nations#GDP|Nation GDP]]
|-
| Nuking Faction Commits [[Factions#Atrocity|Atrocities]] || colspan=2 | 1 per 100k {{TV|pop}} killed (rounded down).
|
* Multiply by 10 if nuke launcher is not on the defending side of any war where the target nation is on the attacking side.
** ...seems to apply for self-nukes too??
{{SpoilerBox|Alien-Related}}
** Does not apply if the target region is owned by the [[Aliens#Alien_Administration|Alien Nation]].
{{SpoilerBoxEnd}}
* Capped between 1 and 20.
|-
| All Human Nations' GDP || -25% × [[Nations#GDP_Per_Region|Region GDP]] / Global GDP + (0% to -2%) || -5% × [[Nations#GDP_Per_Region|Region GDP]] / Global GDP + (0% to -2%) || None
|-
| [[Family Ties]] Trait Effect || colspan=2 | {{TV|loyalty|-10}} || Multiply by 2 if Councilor's Faction launched the nuke.
|-
| Target Region is {{icon|core economic region|bgcolor=DarkSlateGray}}Core Economic || Remove {{icon|core economic region|bgcolor=DarkSlateGray}}Core Economic status || Nothing || None
|-
| All Human Nations' [[Nations#GDP|GDP]] || -2.5% + (0% to -2%) || N/A || If Target Region just lost {{icon|core economic region|bgcolor=DarkSlateGray}}Core Economic status.
|-
| Target Region is {{icon|oil region}}Core Oil or {{icon|resource region}}Core Mining || Remove {{icon|oil region}}Core Oil or {{icon|resource region}}Core Mining status || Nothing || None
|-
| All Human Nations' [[Nations#GDP|GDP]] || -1.5% + (0% to -2%) || N/A || If Target Region just lost {{icon|oil region}}Core Oil or {{icon|resource region}}Core Mining status.
|-
| Target Nation [[Nations#Priorities|Priorities]] || colspan=2| Set to 0 || Except {{icon|spoils}}Spoils, {{icon|unity}}Unity, and {{icon|oppression}}Oppression.
|-
| rowspan=2 | Destroy Space Assets in Target Region || colspan=2 | All {{icon|boost}}[[Nations#Boost|Boost]], {{icon|mc}}[[Nations#Mission_Control|Mission Control]] , and {{icon|sto defense|bgcolor=DarkSlateGray}}[[Nations#Space_Defenses|Space Defenses]] || If Target Nation is NOT Nuke Launcher
|-
| N/A || All {{icon|boost}}[[Nations#Boost|Boost]] and {{icon|sto defense|bgcolor=DarkSlateGray}}[[Nations#Space_Defenses|Space Defenses]], just 1 {{icon|mc}}[[Nations#Mission_Control|Mission Control]] || If Target Nation is Nuke Launcher
|-
| Target Nation {{icon|funding}}[[Nations#Funding|Funding]] || N/A || -50% × [[Nations#GDP_Per_Region|Region GDP]] / [[Nations#GDP|Nation GDP]] || If Target Nation is Nuke Launcher
|-
| rowspan=7 | Health of Each Army in Target Region || colspan=2 | Instant Death || For the Strongest<ref>The strongest army is the army whose health % × Base {{TV|miltech}} is the highest.</ref> Army that is not Ally of Nuker<ref name=allyofnuker>An army is an ally of the nuker if any of the following are true:
* The army is owned by the nuking nation.
* The army is owned by an ally of the nuking nation.
* The army is owned by the nuking faction and not a [[Aliens#Megafauna|Megafauna]].</ref>.
|-
| colspan=2 | Min(0%, (-100% + (1% to 5%) × (Base {{icon|miltech}}MilTech - 3.79)) × 0.140625) || For each [[Aliens#Invader Armies|Alien Invader Army]] that is not Ally of Nuker<ref name=allyofnuker />.
|-
| colspan=2 | Min(0%, -100% + (1% to 5%) × Max(0, Base {{icon|miltech}}MilTech - 3.79) × 0.75 if [[Army Nuclear Hardening]] researched × 0.140625 if working for Aliens) || 50% chance for each Human army that is not Ally of Nuker<ref name=allyofnuker />.
|-
| colspan=2 | -100% × 0.75 if [[Army Nuclear Hardening]] researched × 0.140625 if working for Aliens || The other 50% chance for each Human army that is not Ally of Nuker<ref name=allyofnuker />.
|-
| colspan=2 | Min(0%, -100% + (1% to 5%) × Max(0, Base {{icon|miltech}}MilTech - 3.79)) || 50% chance for each Megafauna army.
|-
| colspan=2 | -100% || The other 50% chance for each [[Aliens#Megafauna|Megafauna]] army.
|-
| colspan=2 | -100% / (48 to 52) || For each army that is Ally of Nuker<ref name=allyofnuker />.
|-
| Each [[Councilors|Councilor]] in Target Region || colspan=2 | 50% Chance to die || [[Survivor]] trait gives immunity.
|-
| [[Aliens#Xenoforming|Alien Xenoforming]] || colspan=2 | Set to 0 Xenoflora Growth Levels || None
|-
| Add [[Climate Change|Aerosols]] || colspan=2 | 0.00777 || Multiply by Region Area (km²) / 10000km² if Region is an Island smaller than 10000km².
|-
| colspan=4 | Target Region Gains 1 Layer of Nuclear Fallout
|}

<references />

== Orbital Bombardment ==

[[Spaceships]] with certain weapon modules can bombard hostile armies from orbit.

See [[Fleets#Orbital_Bombardment]] for more details.

{{Mechanics_Navbox}}

Terrestrial Warfare

2026-03-17T19:37:00Z

76561197989421583: Proposition of ==== Simplified Combat Rules ==== including a quick ====== Hit Chance Reference Table ====== to help readers with army combat decision making.

This page mainly discusses the mechanics for fighting terrestrial wars. For a more detailed discussion about starting and ending wars, see [[Foreign Relations#Wars]] instead.

[[Foreign Relations#Wars|Wars]] begin when a [[Councilors|councilor]] for the executive [[Factions|faction]] of one of two [[Foreign Relations#Rivals|Rivals]] selects the [[Foreign Relations#Declaring_Wars|War policy]] against the rival. All war-capable [[Foreign Relations#Alliances|allies]] of the defending rival (with an army or nuclear weapons) join the war. All war-capable allies of the attacker are given the option to join on the attacker's side.

To win a war, an [[Nations#Armies|army]] must occupy the enemy's {{icon|capital|bgcolor=DarkSlateGray}}Capital [[Regions|region]]. At that moment, the war ends, triggering a [[Foreign Relations#War_Conquest|regime change]]. [[Foreign Relations#Claims|Claimed regions]] change hands to the occupier and its allies. If any of the invaded nation remains, its control point owners are replaced with those of the victor. Some of the nation's stats change when a new regime is installed, sometimes in unpredictable ways, but the new ruling faction will be able to fund [[Nations#Direct_Investment|Direct Investments]] into the nation at greatly reduced {{TV|influence}} cost for a period of one year. Unoccupied [[Regions]] and surviving enemy armies will contribute to greater {{TV|unrest}} following a regime change.

Wars may also end with a [[Foreign Relations#Seeking_Peace|simple peace]] where both sides return to the prewar status quo.

== Armies ==

[[Nations#Armies|Armies]] represent multiple modern divisions that are capable of gaining and holding territory in other [[Nations]]. Control of an army is gained after councilors gain at least partial control of a nation. Most [[Nations]] don't have armies at the campaign start, but [[Nations]] with sufficient {{TV|pop}} can build new ones with enough investment into the {{TV|build army}}. While powerful, armies are a drag on a nation's {{icon|ip|bgcolor=DarkSlateGray}}economic development and remain subject to the international relations of their home countries, which too can be managed with sufficient control of a nation.

Armies have a [[File:ICO army HQ.png|20px]]headquarters region in their home nation. If located there, they incur a smaller cost to the nation's {{icon|ip|bgcolor=DarkSlateGray}}economic development.

Armies rely on two key values: its parent nation's {{TV|miltech}} level and its strength. The strength value measures how much damage the army has taken. Armies usually passively and freely repair themselves when not fighting in a friendly region.

Some armies have a {{icon|navy}}[[Nations#Navies|Navy]] upgrade that allows them to transit oceans. During wartime, a nation's navies can only cross the water if the nation has naval superiority over its foes. Only larger or wealthier [[Nations]] have the capability to {{icon|build navy}}build and project power with {{icon|navy}}navies.

=== Naval Freedom ===

For each [[Foreign Relations#Wars|war]], the game computes for each side the sum of the {{TV|miltech}} of the armies that have a navy upgrade. If one side has a higher sum than the other, then the other side of the war is blockaded: all of its nations no longer have Naval Freedom.

As a result, a nation only has Naval Freedom if it is not blockaded in any of the wars that it is involved in.

Notably, since wars can get very messy, with multiple overlapping wars, it is actually entirely possible for all nations to lose their Naval Freedom.

Consider a simple example with 3 nations: A, B, and C, such that:
* A has a single navy with {{TV|miltech|3}}.
* B has a single navy with {{TV|miltech|2}}.
* C has a single navy with {{TV|miltech|2}}.

Suppose there are three overlapping wars X, Y, and Z, such that:
* War X pits A against B.
* War Y pits A against C.
* War Z pits A against B and C.

Then the result would be:
* War X blockades B, since A's 3 naval score beats B's 2 naval score.
* War Y blockades C, since A's 3 naval score beats C's 2 naval score.
* War Z blockades A, since A's 3 naval score is beaten by the combined naval score of B's 2 naval score added to C's 2 naval score = 4 naval score.

So all 3 nations have no Naval Freedom.

=== Army Movement ===

Armies are allowed to be in any region R such that one of the following is true:
* R belongs to the army's home nation.
* R belongs to a nation that is [[Foreign Relations#Alliances|allied]] to the army's home nation.
* R belongs to a nation that is [[Foreign Relations#Wars|at war]] with the army's home nation.

An army can directly travel from any region R1 to any region R2 such that at least one of the following is true:
* R1 and R2 are adjacent.<ref name=adjacent>Note: Certain research projects can make pairs of regions become adjacent.</ref>
* R1 and R2 are adjacent only for friendly armies<ref name=adjacent />, and both R1 and R2 belong to nation(s) that are not at war with the army's home nation.
* All of the following are true:
** R1 and R2 both currently have [[Regions#World_Ocean_Access|world ocean access]].
** The army's home nation has [[Terrestrial_Warfare#Naval_Freedom|naval freedom]].
** Either the army does not need to travel between the Black Sea and the World Ocean, or the army's home nation has access to the Turkish Strait.

A nation has Turkish Strait access as long as one of the following is true:
* It is not at war with the nation that owns the Istanbul region.
* The Istanbul region is fully occupied.

<references />

==== Land Movement ====

The time needed for an army to travel directly between two adjacent regions without using a navy is calculated as follows:
<pre> Duration (days) = Distance (km) / 300 (km/day) * 4 / Miltech </pre>

But this value is affected by the following multipliers:
{| class="wikitable sortable" style="text-align:center;"
|-
! rowspan=2| Condition(s) !! colspan=3|Multiplier Value When:
|-
! Only Origin Region is Small<ref name=small>A region is small if it is smaller than 150000km².</ref> !! Only Destination Region is Small<ref name=small />!! Otherwise
|-
| Origin Region is not friendly OR Origin Region has enemy armies || 5 ^ 0.2 || 5 ^ 0.8 || 5 ^ 0.5
|-
| (Origin Region is not friendly OR Origin Region has enemy armies) AND Origin Region is {{icon|rugged}}Rugged || 1.5 ^ 0.2 || 1.5 ^ 0.8 || 1.5 ^ 0.5
|-
| Origin Region is friendly AND Origin Region has no enemy armies AND Origin Region is {{icon|rugged}}Rugged || 1.25 ^ 0.2 || 1.25 ^ 0.8 || 1.25 ^ 0.5
|-
| Origin Region is friendly AND Origin Region has no enemy armies AND Origin Nation has {{TV|unrest|>5}} || (1 + (Origin Nation {{TV|unrest}} - 5) / 6.5) ^ 0.2 || (1 + (Origin Nation {{TV|unrest}} - 5) / 6.5) ^ 0.8 || (1 + (Origin Nation {{TV|unrest}} - 5) / 6.5) ^ 0.5
|-
| Origin Region is a {{icon|colony|bgcolor=DarkSlateGray}}Colony || 1.5 ^ 0.2 || 1.5 ^ 0.8 || 1.5 ^ 0.5
|-
| Destination Region is not friendly || 5 ^ 0.8 || 5 ^ 0.2 || 5 ^ 0.5
|-
| Destination Region is not friendly AND Destination Region is {{icon|rugged}}Rugged || 1.5 ^ 0.8 || 1.5 ^ 0.2 || 1.5 ^ 0.5
|-
| Destination Region is friendly AND Destination Region is {{icon|rugged}}Rugged || 1.25 ^ 0.8 || 1.25 ^ 0.2 || 1.25 ^ 0.5
|-
| Destination Region is friendly AND Destination Nation has {{TV|unrest|>5}} || (1 + (Destination Nation {{TV|unrest}} - 5) / 6.5) ^ 0.8 || (1 + (Destination Nation {{TV|unrest}} - 5) / 6.5) ^ 0.2 || (1 + (Destination Nation {{TV|unrest}} - 5) / 6.5) ^ 0.5
|-
| Destination Region is a {{icon|colony|bgcolor=DarkSlateGray}}Colony || 1.5 ^ 0.8 || 1.5 ^ 0.2 || 1.5 ^ 0.5
|}

<references />

==== Naval Movement ====

The time needed for an army to travel between two regions without using a navy is calculated as follows:
<pre> Duration (days) = (14 days + Distance (km) / 792 (km/day) ) * 4 / Miltech </pre>

But this value is affected by a number of complex calculations that consider the different possible sea routes. In particular, the duration can be significantly affected by whether the army's nation has access to the Suez and Panama canals.

A nation has canal access as long as one of the following is true:
* It is not at war with the nation that owns the Canal region.
* The Canal region is fully occupied.

The Canal regions are:
* Cairo for the Suez Canal.
* Panama City for the Panama Canal.

=== Army Battle ===

==== Simplified Combat Rules ====

Combat in ''Terra Invicta'' is a comparison of Miltech levels. Higher Miltech means you hit more often and deal more damage. If two forces have equal Miltech, the base hit chance is 50%.

===== 1. Hit Chance (The Accuracy Gap) =====
The game calculates the difference (Δ) between the Attacker's Miltech and the Defender's Miltech.

If Miltechs are equal: 50% Hit Chance.
If you have the advantage: Your hit chance climbs toward 100%.
If you are outclassed: Your hit chance drops toward 0%.

Hit Chance (Advantage)=100%−(50%×0.7751.5×Δ)
Hit Chance (Disadvantage)=50%×0.7751.5×Δ

'''Quick Guide:''' A 1-point Miltech advantage raises your hit chance to roughly 66%. A 2-point advantage raises it to roughly 79%.
====== Hit Chance Reference Table ======

The following table shows the 1vs1 hit chance based on the Miltech difference (Delta = Attacker Miltech - Defender Miltech).

{| class="wikitable" style="text-align: center;"
|-
! Miltech Difference (Delta) !! Hit Chance !! Note
|-
| '''+3.0''' || '''84.1%''' ||
|-
| '''+2.0''' || '''76.7%''' ||
|-
| '''+1.0''' || '''65.9%''' || '''Strong offensive edge.'''
|-
| +0.8 || 63.2% ||
|-
| +0.6 || 60.3% ||
|-
| +0.4 || 57.1% ||
|-
| +0.2 || 53.7% ||
|-
| '''0.0''' || '''50.0%''' || '''Even match; coin-flip odds.'''
|-
| -0.2 || 46.3% ||
|-
| -0.4 || 42.9% ||
|-
| -0.6 || 39.7% ||
|-
| -0.8 || 36.8% ||
|-
| '''-1.0''' || '''34.1%''' || '''Struggling to land hits.'''
|-
| '''-2.0''' || '''23.3%''' ||
|-
| '''-3.0''' || '''15.9%''' ||
|}

===== 2. Damage Formulas =====
Damage is calculated as a percentage of the defender’s Max Health.

====== Army vs. Army ======
When an army hits another army, it '''deals roughly 10% of its Miltech in percentage of defender’s Max Health'''.

Base Damage: Miltech × 0.1 (±20%)

Variance: ±20% is the game simulating a damage range mechanic.

Critical Hit: Usually 1x. Increases to 3x if the attacker is at full health and the region is unoccupied (an "Ambush"), or by a small random chance based on the total number of armies in the fight.

====== Region vs. Army ======
Region defenses (fortifications/militia) fire every day at every hostile army. They deal less base damage but have much higher "Critical" lethality.

Base Damage: Region Miltech × 0.0225

The "Lethality" Multiplier: If an army is at full health and the region is unoccupied, the region can deal a massive 100x damage critical hit.

Overwhelmed Defenses: If more hostile armies are present than friendly armies, the region's damage output is reduced.

====== Occupying a Region (Army vs. Region) ======
When an army hits region defenses, it increases the Occupation %.

Base Damage: Army Miltech × 0.0225

Advantage Bonus: If your Army Miltech is higher than the region's base tech, you gain occupation faster.

Geography Modifiers: Occupation is slower in regions with huge populations (like Delhi) or massive land areas (like Siberia).

Crowding Penalty: Having too many armies in one spot (more than 1 per 100,000 km2) slows down occupation by up to 50%.

==== Combat Rules ====

Combat occurs whenever an army A is in a [[Regions|region]] R such that at least one of the following is true:
* A's home nation is [[Foreign_Relations#Wars|at war]] with the home nation of another army in R.
* R is partially or fully occupied and A's home nation owns R.
* R is partially or fully occupied and A's home nation is [[Foreign_Relations#Alliances|allies]] with the nation that owns R.
* A's home nation is [[Foreign_Relations#Wars|at war]] with the nation that owns R and R is not fully occupied.
* A's home nation does not exist and R is not fully occupied.
{{SpoilerBox|Alien-Related}}
* There is a [[Aliens#Megafauna|Megafauna Army]] in R that is not owned by the same faction that owns A.
* A's home nation is [[Foreign_Relations#Wars|at war]] with the nation that owns R and A is an [[Aliens#Invader_Armies|Invader Army]] and R is fully occupied by a war alliance that does not include the [[Aliens#Alien_Administration|Alien Nation]].
* A's home nation does not exist and A is an [[Aliens#Invader_Armies|Invader Army]] and R is fully occupied by a war alliance that does not include the [[Aliens#Alien_Administration|Alien Nation]].
* A is a [[Aliens#Megafauna|Megafauna Army]] that is owned by the {{icon|alien}}[[Aliens]] and R is not part of the [[Aliens#Alien_Administration|Alien Nation]] and R is not owned by a nation whose executive is controlled by a faction that has researched [[Xenofauna Harmony]].
* A is a [[Aliens#Megafauna|Megafauna Army]] that is owned by a faction F that is '''not''' the {{icon|alien}}[[Aliens]] and every non-[[Aliens#Megafauna|Megafauna]] army in R that is owned by F is owned by a nation that is [[Foreign_Relations#Wars|at war]] with the nation that owns R.
{{SpoilerBoxEnd}}

Combat is simulated as a daily exchange of attacks. For each army A:
# If there is an enemy army in the combat region, then A randomly selects one to fire at, preferring to avoid any armies owned by the same faction as A.
# If A is within a region that is hostile to A, then the region defenses fires at A.
# If A did not fire at anyone in the first step AND the region defenses missed its attack on A, then A fires at the region defenses.

Note that this means every army can fire at most one attack per day, but region defenses fire an attack on every hostile army every day.

Every attack has a hit chance that is determined by the gap between the attacker's {{TV|miltech}} and the defender's {{TV|miltech}}. But several modifiers may be applied to each side's {{TV|miltech}}, including but not limited to {{MissionIcon|Advise}}[[Advise|Advising]] [[Councilors]], {{icon|rugged}}rugged terrain bonuses, and damage taken.

When attacks hit, damage is taken, which scales based on the attacker's {{TV|miltech}}. When armies take damage, their health % drops. When region defenses take damage, their occupation % increases.

If a region is fully occupied it ceases fighting, but it can't change hands until the war is concluded. Regional economies and space facilities can take significant [[Regions#Region_Damage|collateral damage]] during fighting, although the rate of damage goes down as {{{TV|miltech}} goes up (representing more precise weaponry). Sufficient collateral damage will count as an [[Factions#Atrocity|atrocity]] by the army's owning faction.

==== Formulas ====

'''Miltech Calculations:'''

{| class="wikitable"
|-
! Factor !! Army Miltech A !! Army Miltech B !! Region Miltech
|-
| Base Miltech || Base Miltech || Base Miltech || Base Miltech
|-
| Councilor {{MissionIcon|Advise}}[[Advise]] Bonus || +0.01 per {{TVS|command}} || +0.01 per {{TVS|command}} || +0.01 per {{TVS|command}}
|-
| LEO Hab Bonus (capped at +0.3) || +0.03 per Military Lab || +0.03 per Military Lab || No Effect
|-
| In Home Nation || +0.2 || +0.2 || No Effect
|-
| In Home Nation AND region is {{icon|rugged}}rugged || +0.2 || +0.2 || +0.2
|-
| In Home Nation AND region is {{icon|core economic region|bgcolor=DarkSlateGray}}core economic || +0.1 || +0.1 || +0.1
|-
| Region is {{icon|rugged}}rugged and [[Mountain Warfare Doctrine]] is researched || +0.125 || +0.125 || +0.125
|-
| Region is {{icon|core economic region|bgcolor=DarkSlateGray}}core economic and [[Urban Warfare Doctrine]] is researched || +0.125 || +0.125 || +0.125
|-
| Army CP is disabled (Abandoned or {{MissionIcon|Crackdown}}[[Crackdown]]ed) || -0.2 || -0.2 || No Effect
|-
| In Allied (or Home) Nation || +0.05 per {{TV|cohesion}} of Allied Nation || No Effect || No Effect
|-
| Home Nation's {{TV|cohesion}} || No Effect || No Effect || +0.05 per {{TV|cohesion}}
|-
| Home Nation's {{TV|unrest}} || No Effect || No Effect || -0.05 per {{TV|unrest}}
|-
| Adjacent Regions belonging to Same Home Nation || No Effect || No Effect || +Fraction of such Regions that are unoccupied and not fighting × Home Nation's Miltech × 0.1 × (1 - 0.05 × Home Nation's {{TV|unrest}})
|-
| Remaining Combat Effectiveness || × (1 - 0.5 × Lost Health %) || × (1 - 0.5 × Lost Health %) || × (1 - 1/3 × Occupation %)
|-
|}

Note: If a nation has not completed the {{TV|found military}}, then its regions have effectively {{TV|miltech|0}} for combat.

'''Hit Chance Calculation:'''
* When an army fires at another army, the attacking army uses its '''Army Miltech A''' as the Attack value, while the defending army uses its '''Army Miltech B''' as the Defense value.
* When region defenses fire at an army, the region defenses use '''Region Miltech''' as the Attack value, while the defending army uses its '''Army Miltech A''' as the Defense value.
* When an army fires at the region defenses, the hit chance is always '''100%'''. (But the army only fires if the region defenses missed their attack.)

{| class="wikitable"
|-
! Condition
! Formula
|-
| Defense ≥ Attack
| <code>50% × 0.775^(1.5 × (Defense-Attack))</code>
|-
| Attack > Defense
| <code>100% − (50% × 0.775^(1.5 × (Attack-Defense)))</code>
|}

'''Damage taken:'''
When an army successfully lands a hit on another army, the defending army loses X% of its max health, where X calculated as follows:
# Set X to the attacking army's '''Army Miltech A'''.
# Multiply X by 0.1.
# Multiply X by a random value between 0.8 and 1.2.
# Multiply X by a critical multiplier Z, calculated as follows:
## Set Z to 1.
## Y% chance to set Z to 3, where Y is the square of the number of armies in the region that are involved in the war (allied armies that aren't part of the war don't count).
## If the attacking army is at full health and neither army is a [[Aliens#Megafauna|Megafauna]] and the region is 0% occupied, set Z to 3.
# All army damage bonuses from [[Technology|Projects]] are applied to X. (These bonuses are multiplicative and compounding, but often require the defending army to be a specific type of army.)

When the region defenses successfully land a hit on an army, the defending army loses X% of its max health, where X calculated as follows:
# Set X to the region's '''Region Miltech'''.
# Multiply X by 0.0225.
# Multiply X by a random value between 0.8 and 1.2.
# Let Y be the number of region-friendly armies in the region that are involved in the war (allied armies that aren't part of the war don't count) multiplied by the square of the number of region-hostile armies in the region.
# Multiply X by a critical multiplier Z, calculated as follows:
## Set Z to 1.
## Y% chance to set Z to 40.
## If the region is 0% occupied and the defending army is at full health, then set Z to 100.
## If Z is not 100, another Y% chance to set Z to 40.
## If Z is less than 40, (Y% / (100% - Y%)) chance to set Z to 5.
# All army damage bonuses from [[Technology|Projects]] are applied to X, except for bonuses against [[Aliens#Megafauna|Megafauna]]. (These bonuses are multiplicative and compounding, but often require the defending army to be a specific type of army.)
# Let H be the sum of the Remaining Combat Effectiveness multipliers of every region-hostile army in the region.
# Let F be the sum of the Remaining Combat Effectiveness multipliers of every region-friendly army in the region that is involved in the war (allied armies that aren't part of the war don't count).
# If H - F is more than 0, then multiply X by 1 - (H - F) / (H - F + 2).
# (1 - Region occupation % by defending army's home nation / H) chance to multiply X by 2.

If this last (1 - Region occupation % by defending army's home nation / H) chance fails, the region occupation % by the defending army's home nation actually '''decreases''' by D%, where D is calculated as follows:
# Set D to the region's Region Miltech.
# Multiply D by 0.0225.
# Multiply D by a random value between 0.8 and 1.2.
# Divide D by the number of region-hostile armies in the region.
# Multiply D by the '''Region Combat Action Multiplier''', which is calculated as 2 / (Region Population ^ 0.75 / Game Start Mean Average Region Population ^ 0.75 + Region Area ^ 0.5 / Median Region Area ^ 0.5).
# If D > 10, then set D to 10.

When an army hits the region defenses, the attacking army's home nation increases its occupation % of the region by X%, where X is calculated as follows:
# Set X to the attacking army's '''Army Miltech A'''.
# Let G be X - the defending region's home nation's base {{TV|miltech}} - the Councilor {{MissionIcon|Advise}}[[Advise]] Bonus for the defending region's home nation.
# If G > 0 then add G to X.
# Multiply X by 0.0225.
# Multiply X by a random value between 0.8 and 1.2.
# Multiply X by the '''Region Combat Action Multiplier''', which is calculated as 2 / (Region Population ^ 0.75 / Game Start Mean Average Region Population ^ 0.75 + Region Area ^ 0.5 / Median Region Area ^ 0.5).
# Multiply X by a critical multiplier Z, calculated as follows:
## Set Z to 1.
## Y% chance to set Z to 40.
## If the region is 0% occupied and the defending army is at full health, then set Z to 100.
## If Z is not 100, another Y% chance to set Z to 40.
## If Z is less than 40, (Y% / (100% - Y%)) chance to set Z to 5.
# Let C be the number of region-hostile armies in the region - the region area / 100000km².
# If C > 0, then multiply X by Max(1 - C * 0.02, 0.5)
# If X > 10, then set X to 10.

===

=== Army Operations ===
The faction that controls an army can conduct operations with it. They are:
{| class="wikitable"
! Operation !! width=85% | Effects
|-
| [[File:ICO DeployArmyOperation on.png|40px]] Deploy Army
| Move this Army to an adjacent region, including those of allies or wartime enemies. Armies will engage in battle with enemy armies and occupy enemy regions.
|-
| [[File:ICO DeployArmiesOperation on.png|40px]] Deploy Armies
| Move all stacked armies to an adjacent region, including those of allies or wartime enemies. Armies will engage in battle with enemy armies and occupy enemy regions.
|-
| [[File:ICO AssaultAlienAssetOperation on.png|40px]] Assault Alien Asset
| Launch an assault on a fixed alien target.
|-
| [[File:ICO AssaultSpaceFacilityOperation on.png|40px]] Assault Space Facility
| Destroy a fixed space facility in the region.
|-
| [[File:ICO RazeRegionOperation on.png|40px]] Raze Region
| Launch a general attack on economic and civilian targets in this region. Commits 5 to 25 [[Factions#Atrocity|atrocities]].
|-
| [[File:ICO ArmyGoHomeOperation on.png|40px]] Airlift Home
| Return this army to its home region during peacetime. Operation will not complete if home nation is at war.
|-
| [[File:ICO CancelArmyOperation on.png|40px]] Cancel Operation
| Cancel current operation for this Army. Army will resume fighting if enemies are present.
|}

'''Wiki Help wanted''': Look up the in-game image and description for the Army Annex Region operation and upload both here!

==== Annex Region ====

The game mechanics for army annex operations are explained here [[Foreign Relations#War_Annexation]].

==== Raze Region ====

See [[Regions#Region_Damage]].

==== Assault Alien Asset ====

{| class="wikitable"
|+ Damage Taken by {{TV|armies}} when they Assault Alien Assets
|-
! rowspan=2 | Mission Outcome !! colspan=2 | Type of Alien Asset
|-
! [[Aliens#Alien_Xenoforming|Xenoflora]] !! Other
|-
| Critical Failure || (30% to 150%) / Base {{TV|miltech}} || (150% to 300%) / Base {{TV|miltech}}
|-
| Normal Failure || (15% to 112.5%) / Base {{TV|miltech}} || (75% to 225%) / Base {{TV|miltech}}
|-
| Normal Success || (0% to 75%) / Base {{TV|miltech}} || (0% to 150%) / Base {{TV|miltech}}
|-
| Critical Success || (0% to 15%) / Base {{TV|miltech}} || (0% to 30%) / Base {{TV|miltech}}
|}

Note: Base {{TV|miltech}} is simply the army's home nation's {{TV|miltech}}, with all modifiers ignored.

See [[Aliens]] for spoilers on the different types of alien assets that can be assaulted, as well as the consequences of such assaults.

=== Army Healing ===

An injured human army will passively heal over time when all of the following conditions are true:
* It is in a friendly region<ref>A region owned by its home nation or a nation allied to its home nation</ref>.
* The region is currently not occupied or being occupied.
* It is not in battle with other armies.
* It is not currently performing an operation.

The % health that gets healed each day is calculated as follows:
# 0.5% Base.
# +0.5% more if the faction that controls the army also controls the [[Nations#Control_Point_Types|Defense Sector Control Point]] of the army's home nation.
# +0.5% more if the army is in its home nation.
# +0.5% more if the army is in its home region.
# Multiply the total by (1 - (Currently Healing Human Armies of Home Nation / (Total Human Armies of Home Nation + 1))).
#* Note: This step is currently bugged to never occur.
# +0.5% more if the faction that controls the army has researched the [[Rapid Repairing Materials]] project.
# +0.5% more if the faction that controls the army has researched the [[Predictive Logistics Systems]] project.

{{SpoilerBox|Alien-Related}}
Human armies that are owned by the {{icon|alien}}[[Aliens]] still follow the same healing rules.

But for the healing mechanics of Alien-related armies, see [[Aliens#Megafauna]] and [[Aliens#Invader_Armies]] instead.
{{SpoilerBoxEnd}}

<references />

=== Army Death ===

Whenever an army dies, multiple effects may occur:

==== Democracy Penalties ====

If the dead army belonged to a democratic human nation, then that nation suffers two penalties:
* A {{TV|cohesion}} loss equal to the nation's {{TV|democracy}} / 10.
* Applies [[Nations#Changing_Public_Opinion|Propaganda]] in the nation for the faction that owned the dead army. Propaganda strength is equal to (0 - the nation's {{TV|democracy}}).

==== Army IP Refund ====

Whenever a human army dies, its home [[Nations|nation]] receives a fraction of its {{TV|IP}} Cost as a refund. This refund is put directly into the {{TV|build army}} and/or {{TV|build navy}}, so it can often result in new {{TV|armies}} and/or {{TV|navies}} being built the next day. Specifically, the refund amounts are calculated as follows:

{| class="wikitable sortable" style="text-align:center;"
|+ Refund Amounts for {{TV|build army}}. Only applies if army did not die by nuke.
|-
! Army Died in Home Nation? !! Refund Amount
|-
| Yes || (30% to 50%) of {{TV|build army}} cost.
|-
| No || (15% to 25%) of {{TV|build army}} cost.
|}

{| class="wikitable sortable" style="text-align:center;"
|+ Refund Amounts for {{TV|build navy}}. Only applies if the dead army had a navy.
|-
! Army Died in Home Nation? !! Home Nation has [[Terrestrial_Warfare#Naval_Freedom|Naval Freedom]]? !! Army Died in Region that currently has [[Regions#World_Ocean_Access|World Ocean Access]]? !! Refund Amount
|-
| Yes || Yes || Yes || (70% to 90%) of {{TV|build navy}} cost.
|-
| Yes || Yes || No || (90% to 110%) of {{TV|build navy}} cost.
|-
| Yes || No || || (20% to 30%) of {{TV|build navy}} cost.
|-
| No || Yes || Yes || (60% to 80%) of {{TV|build navy}} cost.
|-
| No || Yes || No || (80% to 100%) of {{TV|build navy}} cost.
|-
| No || No || || (10% to 20%) of {{TV|build navy}} cost.
|}

==== Complete Milestones ====

If the army is related to the [[Aliens]] in any way, then the faction that kills it may achieve certain milestones from doing so. See [[Aliens]] for details.

==== Hate Vent ====

See [[Diplomacy#Alien_Hate_Vent]].

== Nuclear Warfare ==
Some nations have a number of {{TV|nukes}} available to them. These represent launching multiple strategic nuclear weapons at a target region. Launching nuclear strikes will devastate the economy of a [[Regions|region]] and the enemy {{TV|armies}} within it, although the damage will be somewhat mitigated if a nation is launching strikes on its own or an [[Foreign_Relations#Alliances|ally]]'s territory. Launching factions will be charged with committing one or more [[Factions#Atrocity|atrocities]]. Detonating a sufficient number of nuclear weapons may also have disastrous global effects. A region with {{icon|sto defense}}space defenses cannot be attacked with {{TV|nuke}}.

Nations can develop nuclear weapon with the {{TV|develop atomic bomb}}, which also gives {{TV|nuke|1}}. A nation with nuclear weapon program can build more with the {{TV|nuclear weapons}}.

Nations construct nuclear weapons as a deterrent to enemy invasion. Attempting to conquer a nuclear-armed nation will almost certainly lead to nuclear strikes in retaliation.

=== Valid Targets for a Nuclear Strike ===

Nukes can only be fired at [[Regions]]. The set of regions that a [[Nations|nation]] X can fire a nuke at is computed as follows:
# Add every region that is owned by any nation that is [[Foreign_Relations#Wars|at war]] with X.
# If X does not have a spaceflight program, then remove every region that is not adjacent to X and does not have [[Regions#World_Ocean_Access|ocean access]].
# If X does not have a spaceflight program and does not have [[Terrestrial_Warfare#Naval_Freedom|naval freedom]], then remove every region that is not adjacent to X.
# Add every region owned by X or an [[Foreign_Relations#Alliances|ally]] of X if the region currently contains an army that is owned by any nation that is [[Foreign_Relations#Wars|at war]] with X.
# For every region R, remove R unless one of the following is true:
#* R is owned by X.
#* R is owned by an [[Foreign_Relations#Alliances|ally]] of X.
#* R is owned by a nation that is [[Foreign_Relations#Wars|at war]] with X and R does not have a [[Nations#Space_Defenses|space defense facility]] built.

=== Effects of a Nuclear Strike ===

Launching nuclear weapons will do terrible and lasting damage to the targeted region, destroy any enemy {{TV|armies}} and all space facilities, and surely be seen with horror around the globe.

{| class="wikitable"
|+ Effects of a Nuclear Attack (In Chronological Order)
|-
! Category !! Amount for Offensive Nukes !! Amount for Defensive Nukes !! Modifiers
|-
| Target [[Nations#GDP_Per_Region|Region GDP]] || -52.5% to -87.5% || -15% to -25%
| rowspan=2 |
* [[Urban Armoring]] multiplies amount by 0.8.
* [[Civil Defense Programs]] multiplies amount by 0.8.
|-
| Target {{icon|pop}}[[Nations#Population|Region Population]] || -18.75% to -31.25% || -1.875% to -3.125%
|-
| Target Nation [[Nations#Sustainability|Pollution Multiplier]] || +0.075 to +0.125 || +0.00375 to +0.00625 || Multiplied by [[Nations#GDP_Per_Region|Region GDP]] / [[Nations#GDP|Nation GDP]]
|-
| Nuking Faction Commits [[Factions#Atrocity|Atrocities]] || colspan=2 | 1 per 100k {{TV|pop}} killed (rounded down).
|
* Multiply by 10 if nuke launcher is not on the defending side of any war where the target nation is on the attacking side.
** ...seems to apply for self-nukes too??
{{SpoilerBox|Alien-Related}}
** Does not apply if the target region is owned by the [[Aliens#Alien_Administration|Alien Nation]].
{{SpoilerBoxEnd}}
* Capped between 1 and 20.
|-
| All Human Nations' GDP || -25% × [[Nations#GDP_Per_Region|Region GDP]] / Global GDP + (0% to -2%) || -5% × [[Nations#GDP_Per_Region|Region GDP]] / Global GDP + (0% to -2%) || None
|-
| [[Family Ties]] Trait Effect || colspan=2 | {{TV|loyalty|-10}} || Multiply by 2 if Councilor's Faction launched the nuke.
|-
| Target Region is {{icon|core economic region|bgcolor=DarkSlateGray}}Core Economic || Remove {{icon|core economic region|bgcolor=DarkSlateGray}}Core Economic status || Nothing || None
|-
| All Human Nations' [[Nations#GDP|GDP]] || -2.5% + (0% to -2%) || N/A || If Target Region just lost {{icon|core economic region|bgcolor=DarkSlateGray}}Core Economic status.
|-
| Target Region is {{icon|oil region}}Core Oil or {{icon|resource region}}Core Mining || Remove {{icon|oil region}}Core Oil or {{icon|resource region}}Core Mining status || Nothing || None
|-
| All Human Nations' [[Nations#GDP|GDP]] || -1.5% + (0% to -2%) || N/A || If Target Region just lost {{icon|oil region}}Core Oil or {{icon|resource region}}Core Mining status.
|-
| Target Nation [[Nations#Priorities|Priorities]] || colspan=2| Set to 0 || Except {{icon|spoils}}Spoils, {{icon|unity}}Unity, and {{icon|oppression}}Oppression.
|-
| rowspan=2 | Destroy Space Assets in Target Region || colspan=2 | All {{icon|boost}}[[Nations#Boost|Boost]], {{icon|mc}}[[Nations#Mission_Control|Mission Control]] , and {{icon|sto defense|bgcolor=DarkSlateGray}}[[Nations#Space_Defenses|Space Defenses]] || If Target Nation is NOT Nuke Launcher
|-
| N/A || All {{icon|boost}}[[Nations#Boost|Boost]] and {{icon|sto defense|bgcolor=DarkSlateGray}}[[Nations#Space_Defenses|Space Defenses]], just 1 {{icon|mc}}[[Nations#Mission_Control|Mission Control]] || If Target Nation is Nuke Launcher
|-
| Target Nation {{icon|funding}}[[Nations#Funding|Funding]] || N/A || -50% × [[Nations#GDP_Per_Region|Region GDP]] / [[Nations#GDP|Nation GDP]] || If Target Nation is Nuke Launcher
|-
| rowspan=7 | Health of Each Army in Target Region || colspan=2 | Instant Death || For the Strongest<ref>The strongest army is the army whose health % × Base {{TV|miltech}} is the highest.</ref> Army that is not Ally of Nuker<ref name=allyofnuker>An army is an ally of the nuker if any of the following are true:
* The army is owned by the nuking nation.
* The army is owned by an ally of the nuking nation.
* The army is owned by the nuking faction and not a [[Aliens#Megafauna|Megafauna]].</ref>.
|-
| colspan=2 | Min(0%, (-100% + (1% to 5%) × (Base {{icon|miltech}}MilTech - 3.79)) × 0.140625) || For each [[Aliens#Invader Armies|Alien Invader Army]] that is not Ally of Nuker<ref name=allyofnuker />.
|-
| colspan=2 | Min(0%, -100% + (1% to 5%) × Max(0, Base {{icon|miltech}}MilTech - 3.79) × 0.75 if [[Army Nuclear Hardening]] researched × 0.140625 if working for Aliens) || 50% chance for each Human army that is not Ally of Nuker<ref name=allyofnuker />.
|-
| colspan=2 | -100% × 0.75 if [[Army Nuclear Hardening]] researched × 0.140625 if working for Aliens || The other 50% chance for each Human army that is not Ally of Nuker<ref name=allyofnuker />.
|-
| colspan=2 | Min(0%, -100% + (1% to 5%) × Max(0, Base {{icon|miltech}}MilTech - 3.79)) || 50% chance for each Megafauna army.
|-
| colspan=2 | -100% || The other 50% chance for each [[Aliens#Megafauna|Megafauna]] army.
|-
| colspan=2 | -100% / (48 to 52) || For each army that is Ally of Nuker<ref name=allyofnuker />.
|-
| Each [[Councilors|Councilor]] in Target Region || colspan=2 | 50% Chance to die || [[Survivor]] trait gives immunity.
|-
| [[Aliens#Xenoforming|Alien Xenoforming]] || colspan=2 | Set to 0 Xenoflora Growth Levels || None
|-
| Add [[Climate Change|Aerosols]] || colspan=2 | 0.00777 || Multiply by Region Area (km²) / 10000km² if Region is an Island smaller than 10000km².
|-
| colspan=4 | Target Region Gains 1 Layer of Nuclear Fallout
|}

<references />

== Orbital Bombardment ==

[[Spaceships]] with certain weapon modules can bombard hostile armies from orbit.

See [[Fleets#Orbital_Bombardment]] for more details.

{{Mechanics_Navbox}}