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 without paying an 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.

Army Battles

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 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.

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. Naval armies may move between coastal regions worldwide if no belligerent power has naval superiority.
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. Naval armies may move between coastal regions worldwide if no belligerent power has naval superiority.
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. Counts as an atrocity.
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.

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.

Completing the nuclear weapons priority can add more nuclear attacks for a nation.

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 Resource	Remove Resource status	Nothing	None
All Human Nations' GDP	-1.5% + (0% to -2%)	N/A	If Target Region just lost Resource 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 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 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.