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This article is considered accurate for the current version (2.5) of the game.

As long as there is at least one empire present that is not Fanatic Pacifist.png Fanatic Pacifist, war is an almost inevitable aspect in any game and can be anything from a small border skirmish to a massive interstellar war of conquest.

Wars are how mid-game and end-game borders are usually drawn.

Casus Belli and Wargoals[edit]

In order for an empire to start a war, it needs a Casus Belli – a reason to declare war. Each Casus Belli grants access to at least one type of Wargoal, which represents the purpose of the war.

Casus Belli and Wargoals Requirements Surrender Acceptance Surrender Effect Status Quo Effect
Diplomacy war.png Conquer
Existing claims on the target's systems −10 per system
−100 per colonized system
Loser cedes all systems with Claims to the winner, even if not occupied. All systems occupied by the loser are returned, regardless of Claims. Each side keeps all systems they have occupied if they have claims on them.
Diplomacy isvassal.png Vassalize
Diplomacy istributary.png Make Tributary
Diplomacy istributary.png Make Subsidiary
Demand Subject Status diplomatic action was refused −100 Loser becomes a subject of the winner, along with all its vassals (if any). If the empire is part of a Federation, it will leave it. All systems fully occupied by the attacker will be turned into a subject of the attacker.
Diplomacy opinion.png Humiliate
Diplomacy rivalry.png Rivalry −50 Loser loses all of its Influence.png Influence, gains -33% Influence.png Monthly Influence Gain and -10% Mod pop happiness.png Happiness for 10 years. Winner gains 100 Influence.png Influence. None
Diplomacy force ideology.png Impose Ideology
War Philosophy policy set to Liberation Wars
Neither empire is a Gestalt consciousness.png Gestalt Consciousness
−100 Loser is forced to shift ethics towards those of the winner and will leave a Federation if it's part of one. Its leader is also forced to abdicate. All systems fully occupied by the attacker will be turned into an empire with the attacker's ethics.
Diplomacy integrating.png Independence
Available to Subject empires against Overlords 0 If the subject wins it becomes independent and the former Overlord removes all Claims it had on the former subject's systems. The subject becomes independent but the former Overlord will gain Claims on the former subject's systems.
Diplomacy war.png Plunder
Civic barbaric despoilers.png Barbaric Despoilers civic −25 Loser loses 500 Energy Credits.png Energy and 500 Minerals.png Minerals for every 3 planets they own, rounded up, and capped at 60 planets, for a maximum of 10,000 Minerals.png Minerals and Energy Credits.png Energy gained. Winner will then gain those resources even if the loser didn't have enough. Loser gets -20% reduced Energy Credits.pngMinerals.png production for 10 years. None
Diplomacy commercial pact.png Expel Corporation
No Commercial Pact or Federation present
Corporate empire has at least one Branch Office on the other's planets
−50 Corporate empire closes all Branch Offices on the attacker's planets. Attacker gains 1000 Energy Credits.png Energy per Branch Office. Corporate empire closes all Branch Offices on the attacker's planets. Corporate empire gains 1000 Energy Credits.png Energy per Branch Office.
Hostile Takeover
Diplomacy commercial pact.png Hostile Takeover
Both empires have Auth corporate.png Corporate authority
Target has at least one Branch Office
−75 All Branch Offices are transferred to the victor. If part of a Federation Branch Offices on other members' planets are kept. None
Diplomatic rival mutual icon.png Colossus
Declaring empire has a Colossus −1000 (Total War) If the attacker's Colossus is destroyed total war ends and the war reverts to a normal war. None
Stop Colossus
Diplomatic rival mutual icon.png Stop Colossus
Declaring empire does not have a Colossus
Target empire has a Colossus
−1000 (Total War) If the defender's Colossus is destroyed total war ends and the war reverts to a normal war. None
Diplomacy war.png Cleansing
Civic fanatic purifiers.png Fanatic Purifiers or Civic machine terminator.png Determined Exterminator civic −1000 (Total War) No.png None
Diplomacy war.png Absorption
Civic devouring swarm.png Devouring Swarm civic
Diplomacy war.png Assimilation
Civic machine assimilator.png Driven Assimilator civic
Diplomacy war.png End Threat
Target empire is Civic fanatic purifiers.pngCivic devouring swarm.pngCivic machine terminator.pngCivic machine assimilator.png genocidal or an Awakened Empire
Diplomacy opinion.png Humiliate
Diplomacy opinion.png Stop Atrocities
Diplomacy opinion.png Outlaw AI
Diplomacy opinion.png Cleanse Holy Worlds
Diplomacy opinion.png Decontaminate Border Territories
Only available to Fallen Empires with low opinion
Either the Fallen Empire's demand was refused or they were rivaled
0 The refused demands are enforced. Defeated empire's leaders will be executed if not immortal. Includes Animosity effects. None
Claim the Galatron
Diplomacy closed borders.png Take Galatron
Target empire has the Galatron Relic −40 Winner keeps (or acquires) the Galatron Relic and gains 100 Influence.png Influence. Includes Animosity effects. None
Leviathans.png War in Heaven
Synthetic Dawn.png Machine Uprising
Available to Fallen Empires and AI Rebellions via a Special Event −1000 (Total War) No.png None

Once a war is declared, the targeted empire has a year to choose its Wargoals. However, certain wargoals will automatically cause the target to issue certain counter wargoals if chosen (As an example; The "Independence" wargoal will automatically cause the targeted empire to issue the "Remain Overlord" wargoal).

Casus Belli with −1000 surrender acceptance lead to a Total War. Total Wars do not require claims and occupied systems automatically change ownership during a Total War. Their new owner will be the participant with the highest claim count on it or the occupier if none of his allies claim this system. If an empire loses all its colonized systems during a Total War all its Starbases in uncolonized systems are removed, making the territory neutral again.


While Casus Belli and Wargoals represent the purpose of a war, claims represent territorial ambitions—the systems which will be controlled by the victor. Which systems can be claimed depends on an empire's War Philosophy policy, with the Unrestricted Warfare philosophy allowing for the claiming of any system not owned by a fellow Federation member. It is possible to claim the same system multiple times to gain a stronger claim on it, which can outbid the competing claims of allies when going to war together. If multiple empires have equal-strength claims on a system the oldest claim is considered the strongest. In general claims are expensive in the early game and become less so later on to allow for more decisive wars to be fought. Claims cannot be rescinded while at war.

Claims cost Influence.png influence, the base cost being 50, modified by the following:

  • +25 per hyperlane distance from owned territory
  • +25 if the system has at least a lvl 1 Starbase (i.e. not just an Outpost)
  • +25 if the system is colonized
  • +100% during offensive war
  • –10% Agenda Expansionist Overtures agenda
  • –10% Tech interstellar campaigns.png Interstellar Campaigns technology
  • –10% Tech galactic campaigns.png Galactic Campaigns technology
  • –10% Civic nationalistic zeal.png Nationalistic Zeal civic
  • –10% Militarist.png Militarist
  • –20% Fanatic Militarist.png Fanatic Militarist
  • –20% Ap interstellar dominion.png Interstellar Dominion ascension perk
  • –20% Diplomacy rivalry.png Rivalry

During defensive wars, claims can be made for any system by the defender, regardless of the War Philosophy policy. Any system lost by any side during a conquest war or total war will give the former owner a claim on it.

Winning war with any non-conquest wargoals will always enforce all claims made by the winning side empires first, regardless of whether these systems were occupied. So for example, winning war with subjugation wargoal against other empire(s) will make it (and any of its allies) lose all systems that have claims on them, including ones made by the now-overlord empire, and only then become a vassal, with territory reduced like that and free claims of strength 10 on all lost systems.

Federation Warfare[edit]

The Federation is the more serious counterpart of the Defensive pact and the inviting attackers mechanic. While it does offer a unique amount of defensive cooperation, builds trust and allows military cooperation using the federation fleet, establishing a conquest strategy can be made very difficult because of the need for unanimous consent of the members to declare war, and each member's expectation of a fair share of spoils from each war. The empire that wishes to declare war can ask the other federation members for their war goals by using the "Suggest Demands" button. However, AI empires will be very hesitant to declare war on empires that are much stronger than them or have very powerful allies. In that case, the "Suggest Demands" button will not give any results.

One exception to this are wars of liberation or to a lesser extent vassalization: usually AI will agree to a liberation war even if all the war goals are assigned to the player. The resulting splinter empire could then be vassalized and later integrated by the player.

In case a federation member is attacked, all allies automatically join the war as defenders without need for a further declaration of war. In this case, the member being attacked has a free hand in choosing federation war goals, which might be all in its own favor.

For empires that are not members of a given federation, Federation Association Status functions as a Non-Aggression Pact with all members of the respective federation. The AI is very unlikely to cancel Association Status once trust has been built on both sides. This can usually be broken by rivaling or insulting the non-member party, until it cancels the agreement on its own. Therefore, care should be taken with granting Association Status to empires that the player may want to attack in the future.

War Exhaustion[edit]

War Exhaustion goes from 0% to 100%, and measures the total weariness and attrition suffered by all empires on one side in a war. War Exhaustion goes up from suffering losses during Space and Ground Warfare, destruction of planets (either from Colossus weapons or Bombardment armageddon.png Armageddon Bombardment), and a passive accumulation over time called Attrition. When a side's War Exhaustion hits 100% they can be forced into a Status Quo peace after 24 months. The speed at which War Exhaustion accumulates is influenced by factors such as ethics, traditions, technology and the amount of claims being pressed - an empire that is fighting to hold onto a handful of border systems will tire faster in a a costly conflict than one whose very independence is being threatened. War Exhaustion also means that an Empire that is losing a war can still fight to minimize their territorial losses by inflicting high War Exhaustion on the enemy.

War Exhaust Gain can be reduced by the following:

Source Reduction
Civic media conglomerate.png Media Conglomerate civic -5%
Civic nationalistic zeal.png Nationalistic Zeal civic -10%
Tech interstellar campaigns.png Interstellar Campaigns technology -10%
Tech galactic campaigns.png Galactic Campaigns technology -10%
Gestalt consciousness.png Gestalt Consciousness -20%

Ending Wars[edit]

Wars can end in two ways: With the surrender of either side or with a negotiated Status Quo peace.

Surrender means that the victor's Wargoal is enforced, any claims the winning side has on the losing side are automatically ceded regardless of occupation status and the defeated empire is forced to keep borders open towards the attacker for 10 years. All wars except those of independence have a negative surrender acceptance, which are countered by factors such as Relative Navy Strength (up to +50), War Exhaustion (up to +100) and Occupation Percentage (up to +100). If an empire and all of its allies (if any) has lost control of all of its systems and/or planets during the war, then a surrender will occur automatically.

Status Quo means that the war has reached a point where neither side is able to score a decisive victory against the other or all wargoals have been achieved decisively before any major battles took place, and both sides agree to cease hostilities and settle for whatever gains or losses they have acquired/suffered. Under a Status Quo peace, all fully occupied systems claimed by a belligerent empire are ceded to the belligerent with the strongest Claim. In the case of a tie, whoever has the oldest claim on the system is considered the stronger claimant. In addition both sides must keep their borders open towards each other for 10 years. Since AI won't surrender to a Total War, they can end only in Status Quo or the destruction of one empire. Status Quo can be enforced by any side as soon as 24 months passed since the opposing side reached 100% War Exhaustion and if both sides reach 100% War Exhaustion the Status Quo is enforced automatically after 24 months.

War Names[edit]

Wars will always be named after the attacker and the defender, followed by one of the following names depending on the wargoal:

Name Wargoal Other requirements
War Any Offensive war against a Fallen Empire
  • Federation War
  • Galactic War
  • Great War
  • War of the Alliances
Any War between two Federations
  • Annexation Attempt
  • Territorial Invasion
  • War of Aggression
  • War of Conquest
  • War of Beliefs
  • War of Ideologies
  • War of Philosophies
Impose Ideology
  • Border War
  • Confrontation
  • War of Humiliation
  • War of Rivalry
Humiliate Regular empire
Punitive Expedition Humiliate Fallen Empire
Anti AI Police Action Outlaw AI
Buffer Zone Creation Decontaminate Border Territories
Holy Purge Cleanse Holy Worlds
Moral Intervention Stop Atrocities
  • Freedom Struggle
  • Independence War
  • Secessionist War
  • War of Independence
  • War of Liberation
  • Servitude Campaign
  • War of Obedience
  • War of Overlordship
  • War of Subjugation
Tributary War Make Tributary Not Auth corporate.png Corporate authority
Enforced Sponsorship Make Tributary Auth corporate.png Corporate authority
The War In Heaven War in Heaven
  • Intervention War
  • Preemptive Action
  • Preventative War
  • Self Protection War
End Threat
  • War of Cleansing
  • Xeno Filth Removal
  • Xeno Purification
Cleansing Civic fanatic purifiers.png Fanatic Purifiers civic
  • Extermination Campaign
  • Organic Disinfection Program
  • Organic Euthanization War
Cleansing Civic machine terminator.png Determined Exterminator civic
  • Absorption War
  • Biomass Accumulation
  • Great Gorging
Machine Uprising Machine Uprising
Subsidiary Acquisition Make Subsidiary
Hostile Takeover Hostile Takeover
  • Embargo War
  • Expulsion War
  • War of Expropriation
Expel Corporation
War for the Galatron Take Galatron
Game concepts