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This article is for the PC version of Stellaris only.

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.

When an AI empire is about to declare war it will first shift fleets towards the border of the target. Targeted empires that have any military intel on the aggressor will receive a warning, with higher military intel levels providing a more accurate estimate on when war will be declared.

Casus belli and wargoalsEdit

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. Once a war is declared, the attacked empire has a year to choose its wargoals.

Status quo effects do not include the defender's capital. In case of status quo the defender will retain its capital system regardless of occupation.

Casus belli and wargoals Requirements Surrender acceptance Victory effect Status quo effect
Claim
  •   Conquer
Existing claims on the target's systems
  • −10 per system
  • −100 per colonized system
Gain control of all systems with claims from the loser, even if not occupied. All systems occupied by the loser are returned, regardless of claims. Each side keeps all systems they have fully occupied if they have claims on them.
Counterattack
  •   Counterattack
  •   Mutual Defense resolution 3
  •    Target is not a member of the Galactic Community
  •   Target is at offensive war with a Galactic Community member
0 Gain control of all systems with claims from the loser, even if not occupied. All systems occupied by the loser are returned, regardless of claims. Each side keeps all systems they have fully occupied if they have claims on them.
Animosity
  •   Humiliate
  • Rivalry
−25 Gain 100   Influence. Loser loses all of its   Influence, gains   −33% monthly influence gain and   10% happiness for 10 years. If the loser had the   Supremacist Diplomatic Stance policy, it is changed to   Belligerent. Each side keeps all systems they have fully occupied if they have claims on them.
Imperial Rebuke
  •   Imperial Rebuke
  • Rivalry and Galactic Emperor
−25 Gain 100   Influence. Loser loses all of its   Influence, gains   −33% monthly influence gain and   10% happiness for 10 years. If the loser had the   Supremacist Diplomatic Stance policy, it is changed to   Belligerent. None
Ideology
  •   Impose Ideology
  •   War philosophy policy set to Liberation Wars
  •    Target is not a Gestalt Consciousness
−100 Loser is forced to shift ethics towards those of the victor and will leave a federation if it's part of one. Its ruler is also replaced. Authority is also shifted to that of the winner unless the winner has   Corporate authority. If at least 1 colonized system is fully occupied, then all systems fully occupied by the attacker will be turned into an empire with the attacker's ethics.
Despoliation
  •   Plunder
  Barbaric Despoilers civic −25 Take 250   Energy and   Minerals from the loser for every planed they control, even if they didn't have enough. Loser gets −20%   Energy and   Minerals for 10 years.

During the war, if the attacking empire invades and captures the capital of the defending empire, there is a 50% chance to steal one of the defenders owned Relics.

Each side keeps all systems they have fully occupied if they have claims on them.
Expropriation
  •   Expel Corporation
  •     No shared Commercial Pact or Federation
  • Corporate empire has at least one branch office on an owned planet
−50 Corporate empire closes all branch offices on the attacker's planets. Gain 1000   Energy per branch office. Corporate empire closes all branch offices on the attacker's planets. Corporate empire gains 1000   Energy per branch office.
Hostile Takeover
  •   Seize Assets
  •   Both empires have Corporate authority
  • Target has at least one branch office
  •    Criminal Heritage civic
−75 All branch offices on planets whose owners have a commercial pact or federation with victor are transferred to the victor. If loser is part of a federation, branch offices on other members' planets are kept. None
Claim the Galatron
  •   Take Galatron
  •   Target empire has the Galatron relic
  •   War philosophy policy set to Unrestricted Wars
  •    Gestalt Consciousness
−40 Gain the Galatron relic and 100   influence. Loser loses all of its   Influence and gains   −33% monthly influence gain and   −10% happiness for 10 years. Attacker gains 1000   energy.
Galatron Access Denied
  •   Seize Galatron
  •   Target empire has the Galatron relic
  • Target empire has closed borders
  •    Driven Assimilator civic
  •      Genocidal
−40 Gain the Galatron relic and 100   influence. Loser loses all of its   Influence and gains   −33% monthly influence gain and   −10% happiness for 10 years. Attacker gains 1000   energy.
Trial of Advancement
  •   Council Seat
  • Target is a member of the Imperial Council
  •   By Trial of Advancement resolution
−100 Replace the loser in the Imperial Council. None
Punishment
  •   Humiliate
  •   Stop Atrocities
  •   Outlaw AI
  •   Cleanse Holy Worlds
  •   Decontaminate Border Territories
  •   Only available to fallen empires
  • Either the fallen empire's demand was refused or they were rivaled
0 The refused demands are enforced. If the losing empire is not a   Gestalt Consciousness, its ruler will also be killed by the winning fallen empire, unless they are the Ancient Caretakers. Loser loses all of its   Influence, gains   −33% monthly influence gain and   10% happiness for 10 years. If the loser had the   Supremacist Diplomatic Stance policy, it is changed to   Belligerent. None

Subjugation wargoalsEdit

Subjugation wargoals seek to end the independence of the targeted empire. If it has any subjects, the effects will apply to them as well. And if the loser is part of a Federation, it will leave it.

Casus belli and wargoals Requirements Surrender acceptance Victory subjugation Status quo effect
Subjugation
  •   Vassalize
  •   Make Tributary
  •   Make Subsidiary
Superior relative power to the target empire.
  •    Driven Assimilator civic
  •      Genocidal
−100   Subject (initial terms of agreement and   Loyalty depend on the Subjugation War Terms policy) if at least 1 colonized system is fully occupied then all systems fully occupied will be turned into a new empire and the victory conditions will be imposed upon it.
Hegemon
  •   Establish Hegemony
  President of a level 3+ Hegemony federation
  •    Target is not in federation
−100   Hegemony member
Scion
  •   Bring Into Fold
  Scion origin −100   Scion of the same overlord
Imposed Inclusion
  •   Bring Into Fold
  Become the Crisis ascension perk −100   Subject (initial terms of agreement and   Loyalty depend on the Subjugation War Terms policy)
Imperial Crusade
  •   Force Into Imperium
  Imperial Crusade resolution −100   Galactic Imperium member

Paired wargoalsEdit

The following wargoals are paired together. If an empire starts a war with either of the paired wargoals the defender will automatically use the other wargoal and cannot pick another one. In case of the Allegiance War casus belli all empires which swore secret fealty to the attacker will join the attacker's side.

Paired wargoals with −1000 surrender acceptance lead to a Total War. In Total Wars, all occupied systems automatically change ownership. Their new owner will be the participant with the highest claim count on it or the occupier if none of their allies claim the system.

Casus belli and wargoal 1 Casus belli and wargoal 2 Requirements Surrender acceptance Victory effect Status quo effect
Subject
  •   Independence
Subject
  •   Assert Overlordship
  •   Subject and overlord
  •   Subject not in a federation with overlord
0 If the subject wins, it becomes independent and the former overlord loses all claims on the former subject's systems. The subject becomes independent and the former overlord gains claims on the former subject's systems.
Secession
  •   Leave Hegemony
Secession
  •   Assert Hegemony
  President refused member to leave federation 0 If the attacker wins, it leaves the federation and the president loses all claims on the former member's systems. If the president wins, both empires gain a temporary   −20 opinion towards each other. The attacker leaves the federation and the president gains claims on the former member's systems.
Allegiance War
  •   Secret Fealty
Allegiance War
  •   Maintain Servitude
  Secret Fealty from one of target's subjects 0 If the attackers win all empires that pledged Secret Fealty to the main attacker will become the attacker's subjects and gain +2.5 Monthly   Loyalty for 10 years. If the defender wins the attacking subjects will gain +5 Monthly   Loyalty for 5 years and cannot pledge Secret Fealty during that time. The subject cannot pledge Secret Fealty for 5 years.
Imperium
  •   Restore Community
Imperium
  •   Crush the Rebellion
  •   Imperium: Spark Rebellion operation
0 Losers gain −60%   Diplomatic Weight for 6 years. If the attackers win the Galactic Imperium becomes the Galactic Community again. If the defenders win the Galactic Imperium gains 100 Authority. All attackers leave the Galactic Imperium and form a federation.
Containment
  •   End Threat
Subjugation
  •   Domination
  Awakened Empire −1000 (Total War) Victory can only be achieved by conquering all colonized systems of the opposition, ending the opposing empire. If a defeated empire had starbases in uncolonized systems that were not conquered, they are removed, making the territory neutral again. Each side keeps all conquered systems.

In case of the Existential Expulsion war goal, uncolonized systems become neutral during the war.

Purification
  •   Cleansing
  Fanatic Purifiers or   Determined Exterminator
Hunger
  •   Absorption
  Devouring Swarm
Sublimation
  •   Assimilation
  Driven Assimilator
Existential Expulsion
  •   Wipe Them Out
  Become the Crisis ascension perk
Colossus
  •   Colossus
Stop Colossus
  •   Stop Colossus
  Either empire has a Colossus
Preemptive War
  •   Preemptive War
Self-Defense
  •   End Threat
  •   Mutual Defense resolution 5
  •    One empire is not a member of the Galactic Community
Crisis War
  •   Crisis War
Crisis War
  •   Crisis War
  •   Declare Crisis resolution
  •    Repeal Crisis resolution
Event
  •   War in Heaven
Event
  •   War in Heaven
  Awakened Empire
Event
  •   Machine Uprising
Event
  •   Machine Uprising
  Creator empire and AI rebellion −1000 (Total War) Victor gains 2000-6000   Unity and 200-600   Influence. Victory can only be achieved by conquering all colonized systems of the opposition, ending the opposing empire. If a defeated empire had starbases in uncolonized systems that were not conquered, they are removed, making the territory neutral again. Each side keeps all conquered systems.

ClaimsEdit

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 the same number of 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 have a base cost of 50   influence, modified by the following:

  1. Additive costs:
    • +25 per hyperlane distance from owned territory
    • +25 if the system has an upgraded   Starbase (i.e. not just an Outpost)
    • +25 if the system is colonized
  2. Additive multipliers:
    • +100%   during an offensive war
    • –10%   Expansionist Overtures   Ruler agenda
    • –10%     Belligerent or   Supremacist Diplomatic Stance policy
    • –10%   Interstellar Campaigns technology
    • –10%   Galactic Campaigns technology
    • –10%   Martial Alliance federation level 2 perk
    • –10%   Militarist ethic
    • –15%   Nationalistic Zeal civic
    • –20%   Fanatic Militarist ethic
    • –20%   Interstellar Dominion ascension perk
    • –20%   Khan's Throne relic
  3. –20%   if the system is owned by a Rival (multiplicative, after other multipliers)

If the modifier reaches a total of –100%, claims then cost 0   influence.

Defenders can freely claim systems owned by their attackers in a defensive war regardless of their War Philosophy policy. Any system lost by any side during a conquest war or total war will give the former owner 10 claims on it.

Winning war with any non-conquest wargoals will always enforce all claims made by the victorious empires before any other effects, regardless of whether these systems were occupied. For example, an empire winning a war with the subjugation wargoal will annex all claimed systems from the loser before making a   Vassal of the loser's remaining systems.

Federation warfareEdit

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 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.

War exhaustionEdit

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   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 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
  Media Conglomerate civic −5%
  Nationalistic Zeal civic −20%
  Interstellar Campaigns technology −10%
  Galactic Campaigns technology −10%
  Belligerent diplomatic stance −10%
  Supremacist diplomatic stance −20%
  Gestalt Consciousness ethic −20%
  Rules of War resolution 2 −5%
  Rules of War resolution 3 −10%
  Rules of War resolution 4 −15%
  Rules of War resolution 5 −20%
  Never Surrender tradition −25%
  Crisis level 2 −75%

Ending warsEdit

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 either side as soon as 24 months have 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 namesEdit

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
Conquer
  • 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
Independence
  • Servitude Campaign
  • War of Obedience
  • War of Overlordship
  • War of Subjugation
Vassalize
Tributary War Make Tributary Not   Corporate authority
Enforced Sponsorship Make Tributary   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   Fanatic Purifiers civic
  • Extermination Campaign
  • Organic Disinfection Program
  • Organic Euthanization War
Cleansing   Determined Exterminator civic
  • Absorption War
  • Biomass Accumulation
  • Great Gorging
Absorption   Devouring Swarm Civic
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
Crisis War Crisis War
  •   Crisis level 5
  • OR
  •   Declare Crisis resolution
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