Warfare

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This article is for the PC version of Stellaris only.

War

Warfare

Space warfare

Land warfare

As long as there is at least one empire present that is not 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

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.

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	Loser cedes all systems with claims to the victor, 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.
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	Loser cedes all systems with claims to the victor, 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.
Subjugation Vassalize Make Tributary Make Subsidiary	Demand Subject Status diplomatic action was refused	−100	Loser becomes a subject of the victor, 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.
Hegemon Establish Hegemony	President of a level 3 Hegemony federation Target is not in federation	−100	Loser becomes a member of the victor's Hegemony	All systems fully occupied by the attacker will be turned into a member of the attacker's Hegemony.
Animosity Humiliate	Rivalry	−50	Victor gains 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 occupied if they have claims on them.
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.	All systems fully occupied by the attacker will be turned into an empire with the attacker's ethics.
Despoliation Plunder	Barbaric Despoilers civic	−25	Loser loses 500 Energy and 500 Minerals for every 3 planets they own, rounded up, and capped at 60 planets, for a maximum of 10,000 Minerals and Energy gained. Victor will then gain those resources even if the loser didn't have enough. Loser gets -20% reduced production for 10 years.	Each side keeps all systems they have occupied if they have claims on them.
Expropriation Expel Corporation	Does not have Corporate Authority No Commercial Pact or Federation present Target is Corporate empire with at least one Branch Office on the other's planets	−50	If the Corporate empire loses it closes all Branch Offices on the attacker's planets and the attacker gains 1000 Energy per Branch Office. If the Corporate empire wins the attacker becomes a Subsidiary of the Corporate empire.	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 Does not have Criminal Syndicate civic Target has at least one Branch Office	−75	All Branch Offices 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
Scion Bring Into Fold	Scion origin	−100	If the Scion wins the loser becomes a subject of the Scion's overlord	All systems fully occupied by the Scion will be turned into a subject of the Scion's overlord.
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 assassinated by the winning Fallen Empire, unless they are the Ancient Caretakers. Includes Animosity effects.	None
Claim the Galatron Take Galatron	Target empire has the Galatron Relic	−40	Victor keeps (or acquires) the Galatron Relic and gains 100 Influence. Includes Animosity effects.	None
Existential Explusion Wipe them Out	Has the Become the Crisis ascension perk.	−1000 (Total War)	The defending empire is 'wiped out.' All starbases are destroyed.	None (Note: Any system taken have their starbases completely destroyed, becoming empty space)

Paired wargoals

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.

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 his allies claim this 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	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 Not a subject to a different overlord	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.
Containment End Threat	Subjugation Assimilation	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.
	Purification Cleansing	Fanatic Purifiers or Determined Exterminator
	Hunger Absorption	Devouring Swarm
	Sublimation Assimilation	Driven Assimilator
Colossus Colossus	Stop Colossus Stop Colossus	Either empire has a Colossus	−1000 (Total War)
Preemptive War Preemptive War	Self-Defense End Threat	Mutual Defense Resolution 5 is passed One empire is not a member of Galactic Community	−1000 (Total War)
Event War in Heaven	Event War in Heaven	Awakened Empire	−1000 (Total War)
Event Machine Uprising	Event Machine Uprising	Creator empire and Machine Uprising	−1000 (Total War)

Claims

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, 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% Expansionist Overtures agenda
• –10% Belligerent or Supremacist policy
• –10% Interstellar Campaigns technology
• –10% Galactic Campaigns technology
• –10% Nationalistic Zeal civic
• –10% Martial Alliance level 2 perk
• –10% Militarist
• –20% Fanatic Militarist
• –20% Interstellar Dominion ascension perk
• –20% Great Khan's Throne relic
• –20% Rivalry (multiplicative, after other multipliers)

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

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

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 exhaustion

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	-10%
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%

Ending wars

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

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
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