Terrestrial Warfare

Wars begin when a councilor for the executive faction of one of two rivals selects the War policy against the rival. All war-capable 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 army must occupy the enemy's capital region. At that moment, the war ends, triggering a regime change event. 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 Direct Investments into the nation at greatly reduced influence cost for a period of one year. Unoccupied regions and surviving enemy armies will contribute to greater unrest following a regime change.

Wars may also end with a simple peace where both sides return to the prewar status quo.

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 population can build new ones with enough investment. While powerful, armies are a drag on a nation's 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 headquarters region in their home nation. If located there, they incur a smaller cost to the nation's economic development.

Armies rely on two key values: its parent nation's Miltech level and its strength. The strength value measures how much damage the army has taken. Armies repair themselves when not fighting in a friendly region.

Some armies have a 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 build and project power with navies.

Naval Freedom

For each war, the game computes for each side the sum of the 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 3 Miltech .
• B has a single navy with 2 Miltech .
• C has a single navy with 2 Miltech .

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 allied to the army's home nation.
• R belongs to a nation that is 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.
• R1 and R2 are adjacent only for friendly armies, 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 world ocean access.
  • The army's home nation has 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.

Land Movement

The time needed for an army to travel between two regions without using a navy is calculated as follows:

 Duration (days) = Distance (km) / 300 (km/day) * 4 / Miltech 

But this value is affected by the following multipliers:

Condition(s)	Multiplier Value When:
	Only Origin Region is Small	Only Destination Region is 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 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 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 >5 Unrest	(1 + (Origin Nation Unrest - 5) / 6.5) ^ 0.2	(1 + (Origin Nation Unrest - 5) / 6.5) ^ 0.8	(1 + (Origin Nation Unrest - 5) / 6.5) ^ 0.5
Origin Region is a 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 Rugged	1.5 ^ 0.8	1.5 ^ 0.2	1.5 ^ 0.5
Destination Region is friendly AND Destination Region is Rugged	1.25 ^ 0.8	1.25 ^ 0.2	1.25 ^ 0.5
Destination Region is friendly AND Destination Nation has >5 Unrest	(1 + (Destination Nation Unrest - 5) / 6.5) ^ 0.8	(1 + (Destination Nation Unrest - 5) / 6.5) ^ 0.2	(1 + (Destination Nation Unrest - 5) / 6.5) ^ 0.5
Destination Region is a Colony	1.5 ^ 0.8	1.5 ^ 0.2	1.5 ^ 0.5

Naval Movement

The time needed for an army to travel between two regions without using a navy is calculated as follows:

 Duration (days) = (14 days + Distance (km) / 792 (km/day) ) * 4 / Miltech 

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

Combat Rules

If at least two enemy armies are in the same region, they will fight. Mechanically, each army takes a shot once a day. Its chance of successfully damaging an enemy army is based on its miltech level, strength, whether any councilors are lending their command attribute to the army's nation via the Advise mission, and whether it on defense and the region has the rugged flag set.

If an army is in an enemy region and no enemy armies are present, it begins occupying the region, battling the local defense forces (who use the nation's tech level and act more or less as an additional army) and taking damage from them. Badly damaged armies will attempt to flee to a safe place without you doing anything, but they can also be destroyed entirely when their strength reaches zero.

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 damage during fighting, although the rate of damage goes down as miltech goes up (representing more precise weaponry). Sufficient damage will count as an atrocity by the army's owning faction.

Formulas

Hit Chance Calculation:

Condition	Formula
Defense ≥ Attack	50% × 2^(-0.55*(Defense-Attack))
Attack > Defense	100% − (50% × 2^(-0.55*(Attack-Defense)))

Attack/Defense Value: (Miltech + Bonus) × (0.5 + 0.5 × Army Health)

Bonus:

• +0.2 base in allied territory
• +0.2 if allied territory is a rugged terrain
• +0.125 if allied/enemy territory is a rugged terrain and Mountain Warfare Doctrine is researched
• +0.1 if allied territory is a core economic region
• +0.125 if allied/enemy territory is a core economic region and Urban Warfare Doctrine is researched
• -0.2 if army CP is crackdown
• Maximum of +0.3 from Military lab modules in Low Earth Orbit
• Councilor advise bonus

Damage taken: If an army is hit, it loses 0.1*Attack% of its life. This damage can be multiplied by 3 if it's a crit. The chance of crit is N^2/100 where N is the number of armies (allied or enemy) in the region.

Army Operations

The faction that controls an army can conduct operations with it. They are:

Operation	Effects
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.
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.
Assault Alien Asset	Launch an assault on a fixed alien target.
Assault Space Facility	Destroy a fixed space facility in the region.
Raze Region	Launch a general attack on economic and civilian targets in this region. Commits 5 to 25 atrocities.
Airlift Home	Return this army to its home region during peacetime. Operation will not complete if home nation is at war.
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!

The game mechanics for army annex operations are explained here Nations#War_Annexation.

Army Healing

An injured army will passively heal over time when all of the following conditions are true:

• It is in a friendly region.
• 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 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 Armies of Home Nation / (Total Armies of Home Nation + 1)).
• +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.

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 Cohesion loss equal to the nation's Government / 10.
• Applies Propaganda in the nation for the faction that owned the dead army. Propaganda strength is equal to (0 - the nation's Government ).

Army IP Refund

Note: As of Version 0.4.90, this mechanic only applies if:

• The killer has a faction.
• The army has miltech < 6 or does not belong to the alien nation.

Both of these look like bugs.

Whenever a human army dies, its home nation receives a fraction of its IP Cost as a refund. This refund is put directly into the Build Army and/or Build Navy priorities, so it can often result in new armies and/or navies being built the next day. Specifically, the refund amounts are calculated as follows:

Refund Amounts for Build Army Priority.

Army Died in Home Nation?	Refund Amount
Yes	(30% to 50%) of Build Army cost.
No	(15% to 25%) of Build Army cost.

Refund Amounts for Build Navy Priority. Only applies if the dead army had a navy.

Army Died in Home Nation?	Home Nation has Naval Freedom?	Army Died in Region that currently has World Ocean Access?	Refund Amount
Yes	Yes	Yes	(70% to 90%) of Build Navy cost.
Yes	Yes	No	(90% to 110%) of Build Navy cost.
Yes	No		(20% to 30%) of Build Navy cost.
No	Yes	Yes	(60% to 80%) of Build Navy cost.
No	Yes	No	(80% to 100%) of Build Navy cost.
No	No		(10% to 20%) of 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 nuclear attacks available to them. These represent launching multiple strategic nuclear weapons at a target region. Launching nuclear strikes will devastate the economy of a region and the enemy armies within it, although the damage will be somewhat mitigated if a nation is launching strikes on its own or an ally's territory. Launching factions will be charged with committing one or more atrocities. Detonating a sufficient number of nuclear weapons may also have disastrous global effects. A region with space defenses cannot be attacked with .

Nations can develop nuclear weapon with develop atomic bomb priority, which grants a strategic nuclear barrage too. A nation with nuclear weapon program can build more with nuclear weapons priority.

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.

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

Effects of a Nuclear Attack (In Chronological Order)

Category	Amount for Offensive Nukes	Amount for Defensive Nukes	Modifiers
Target Region GDP	-52.5% to -87.5%	-15% to -25%	Urban Armoring multiplies amount by 0.8. Civil Defense Programs multiplies amount by 0.8.
Target Region Population	-18.75% to -31.25%	-1.875% to -3.125%
Target Nation Pollution Multiplier	+0.075 to +0.125	+0.00375 to +0.00625	Multiplied by Region GDP / Nation GDP
Nuking Faction Commits Atrocities	1 per 100k Population killed.		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??) Capped between 1 and 20.
All Human Nations' GDP	-25% × Region GDP / Global GDP + (0% to -2%)	-5% × Region GDP / Global GDP + (0% to -2%)	None
Family Ties Trait Effect	-10 Loyalty		Multiply by 2 if Councilor's Faction launched the nuke.
Target Region is Core Economic	Remove Core Economic status	Nothing	None
All Human Nations' GDP	-2.5% + (0% to -2%)	N/A	If Target Region just lost Core Economic status.
Target Region is Core Oil or Core Mining	Remove Core Oil or Core Mining status	Nothing	None
All Human Nations' GDP	-1.5% + (0% to -2%)	N/A	If Target Region just lost Core Oil or Core Mining status.
Target Nation Priorities	Set to 0		Except Spoils , Unity , and Oppression .
Destroy Space Assets in Target Region	All Boost , Mission Control , and Space Defenses		If Target Nation is NOT Nuke Launcher
	N/A	All Boost and Space Defenses , just 1 Mission Control	If Target Nation is Nuke Launcher
Target Nation Funding	N/A	-50% × Region GDP / Nation GDP	If Target Nation is Nuke Launcher
Health of Each Army in Target Region	Instant Death		For the Strongest Army that is not Ally of Nuker.
	Min(0%, (-100% + (1% to 5%) × (Base MilTech - 3.79)) × 0.140625)		For each Alien Invader Army that is not Ally of Nuker.
	Min(0%, -100% + (1% to 5%) × Max(0, Base 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.
	-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.
	Min(0%, -100% + (1% to 5%) × Max(0, Base MilTech - 3.79))		50% chance for each Megafauna army.
	-100%		The other 50% chance for each Megafauna army.
	-100% / (48 to 52)		For each army that is Ally of Nuker.
Each Councilor in Target Region	50% Chance to die		Survivor trait gives immunity.
Alien Xenoforming	Set to 0 Xenoflora Growth Levels		None
Target Region Gains 1 Layer of Nuclear Fallout

Note: 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 Megafauna.

Orbital Bombardment

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