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, 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 wargoals[edit | edit source]
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||Existing claims on the target's systems||
||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 fully occupied if they have claims on them.|
|Counterattack||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 fully occupied if they have claims on them.|
|Subjugation||Superior relative power to the target empire.||−100||Loser becomes a subject of the victor, along with all its vassals (if any). If the empire is part of a federation, they will leave it. 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 by the attacker will be turned into a subject of the attacker. Initial terms of agreement and Loyalty depend on the Subjugation War Terms policy. Partially occupied systems will be returned. Allies will not be subjugated even if fully occupied.|
||−25||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 fully occupied if they have claims on them.|
||−25||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.||None|
|Ideology||−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.||All systems fully occupied by the attacker will be turned into an empire with the attacker's ethics.|
|Punishment||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|
|Despoliation||Barbaric Despoilers civic||−25||Loser loses 250 energy and 250 minerals for every planet they own. Victor will then gain those resources even if the loser 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||−50||Corporate empire closes all branch offices on the attacker's planets. Attacker gains 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||−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||−40||Victor gains 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.|
|Hegemon||President of a level 3+ Hegemony federation||−100||Loser becomes a member of the victor's Hegemony||All systems fully occupied by the attacker will be turned into a new member empire of the attacker's Hegemony.|
|Scion||Scion origin||−100||Loser becomes a subject of the Scion's overlord. If the empire is part of a federation, they will leave it.||All systems fully occupied by the Scion will be turned into a subject of the Scion's overlord.|
|Imposed Inclusion||Become the Crisis ascension perk||−100||Loser becomes a subject of the victor, along with all its vassals (if any). If the empire is part of a federation, they will leave it.||All systems fully occupied by the crisis empire will be turned into a new vassal empire of the attacker.|
|Trial of Advancement||−100||The victor replaces the loser in the Imperial Council.||None|
|Imperial Crusade||Imperial Crusade resolution||−100||Loser joins the Galactic Imperium. If the empire is part of a federation, they will leave it.||All systems fully occupied by members of the Galactic Imperium will be turned into a member of the Galactic Imperium.|
Paired wargoals[edit | edit source]
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 his allies claim this system.
|Casus belli and wargoal 1||Casus belli and wargoal 2||Requirements||Surrender acceptance||Victory effect||Status quo effect|
|Subject||Subject||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||Secession||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||Allegiance War||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||Imperium||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||Subjugation||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||Fanatic Purifiers or Determined Exterminator|
|Existential Expulsion||Become the Crisis ascension perk|
|Colossus||Stop Colossus||Either empire has a Colossus|
|Crisis War||Crisis War|
|Event||Event||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.|
Claims[edit | edit source]
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.
- Additive costs:
- 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
- –20% if the system is owned by a Rival (multiplicative, after other multipliers)
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 warfare[edit | edit source]
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[edit | edit source]
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:
Ending wars[edit | edit source]
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 names[edit | edit source]
Wars will always be named after the attacker and the defender, followed by one of the following names depending on the wargoal: