Casus belli

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Casus belli is a Latin term meaning case of war. In the game, a country with a casus belli (commonly known as just "CB") on another country is deemed to have a valid cause for war. When declaring war, the player is presented with a list of available CBs. They may pick a CB from the list or choose to declare war without a casus belli and accept the penalties of +30 aggressive expansion and -2 Icon stability.png stability (halved with full Diplomatic ideas).

Each casus belli has a particular war goal associated with it, generally either controlling a particular province or winning a certain proportion of battles. Meeting the war goal will cause the war score of whichever side has achieved it to gradually rise (up to a max bonus of 25% at a rate of +0.4% per month). The casus belli also determines what peace terms may be demanded at no or reduced Diplomatic Power cost; additionally, some CBs disallow some peace terms entirely. Extracting additional concessions beyond those of the original CB (unjustified demands) will cost Diplomatic power.png diplomatic power to be demanded.

List of casus belli[edit]

War goals[edit]

Each CB has an associated war goal. This describes what each side has to do to get ticking warscore, i.e. additional warscore over time from having accomplished the goal. Wargoals include:

  • Take province / Defend province: Control a specific province. This may be a province chosen on declaring the war, or the capital. Each side gets ticking warscore as long as they control the target. Neither side gets ticking warscore if a third party (e.g. rebels) controls it.
  • Show superiority: Have at least 10% warscore from battles. No side gets ticking warscore if neither has said warscore from battles
  • Blockade ports: Amount and rate of ticking warscore scales by the proportion of blockading.

Triggered[edit]

A triggered casus belli appears when certain actions are performed (like insulting other countries), and can also be given by events and missions. Triggered casus belli only last for certain amount of time before they expire and are no longer valid.

Casus belli Wargoal Duration Aggressive expansion modifier Prestige modifier DIP power cost modifier Warscore cost modifier Acquisition Affected peace offers
Restoration of Union Take capital 120 months 100% 100% 100% 100% Given to senior personal union partner when a junior partner becomes independent
  • Form personal union
Defected Province Take target province 12 months 100% 200% 100% 50% When a province defects due to rebels
  • Cede province
    • Only on province defected in last 12 months
Canceled Loan Superiority 12 months 100% 200% 100% 75% Given to debtor when creditor defaults on a loan
This used to be such an easy way to get a CB that AI always refuses loans since 1.4.
  • Gold
  • Concede defeat
  • Transfer trade power
Discovered Spy Superiority 12 months 100% 200% 100% 75% Given by two Japanese events involving ninja
  • Revoke core
  • Gold
  • Concede defeat
Disloyal Vassal Take capital 120 months 100% 200% 100% 50% Given to overlord when a vassal breaks free
  • Demand vassalization
  • Demand become protectorate
Imperial Liberation Take target province 120 months 100% 200% 100% 75% Given to the Emperor when an HRE member state is annexed
  • Cede province
    • Only on provinces inside HRE
  • Release vassals
  • Release country
  • Return core
Diplomatic Insult Superiority 12 months 100% 200% 100% 75% By event and the "Send Insult" diplomatic action
  • Revoke core
  • Gold
  • Concede defeat
  • Humiliation
Dishonored Call Superiority 36 months 100% 200% 100% 75% When an ally refuses a call to arms
  • Revoke core
  • Gold
  • Concede defeat
  • Humiliation
Subjugation Take capital 120 months 100% 200% 100% 50% From vassalization missions
Note that some "Subjugate X" missions actually require you to annex them. Pay attention to the mission objectives!
  • Demand vassalization
  • Demand become protectorate
Obscure Documents Take capital 12 months 100% 100% 100% 150% By event
  • Form personal union
Religious Unity Take capital 24 months 100% 200% 100% 75% Given to the emperor when an HRE member refuses the emperor's demand for religious conformance
  • Force change religion
Border Friction Take target province 12 months 75% 100% 100% 75% Some events
Border friction events generally give claims. One that gives this CB is the "Cossack Aggression" event chain.
  • Concede defeat
  • Cede province
    • Only on non-capital provinces bordering your own
Trade War Superiority 24 months 100% 200% 100% 75% By event
Not to be confused with Trade Dispute or Trade Conflict.
  • Revoke core
  • Gold
  • Concede defeat
  • Transfer trade power
  • Can't:
    • Full annexation
    • Cede province
    • Return core
    • Revoke core
    • Release vassal
    • Liberate country
    • Force vassalization
    • Force protectorate
    • Form personal union
Trade Conflict Blockade ports 24 months 100% 100% 100% 100% Via the "Justify Trade Conflict" covert action.
Not available to Merchant Republics (they get their own version, see below).
  • Gold
  • Concede defeat
  • Transfer trade power
    • Costs half amount of warscore
  • Can't:
    • Full annexation
    • Cede province
    • Return core
    • Revoke core
    • Release vassal
    • Liberate country
    • Force vassalization
    • Force protectorate
    • Form personal union
Trade Conflict (trade league) Blockade ports 24 months 100% 100% 100% 100% Available to the leader of a trade league against countries they could otherwise justify a trade conflict against.
  • Gold
  • Concede defeat
  • Transfer trade power
  • Can't:
    • Full annexation
    • Cede province
    • Return core
    • Revoke core
    • Release vassal
    • Liberate country
    • Force vassalization
    • Force protectorate
    • Form personal union
Annexation War Take capital 24 months 50% 100% 100% 100% Given by a few flavour events
  • Full annexation
    • Allows annexation regardless of total warscore cost
  • Demand Province
    • Only on provinces which you have claim on
Government Form War Take capital 120 months 75% 100% 100% 100% By event (Milan's neighbours when it becomes an Ambrosian Republic)
  • Force change government type
  • Demand Province
    • Only on provinces which you have claim or core, or borders

Automatic[edit]

An automatic casus belli is given when certain conditions between you and the defender are met. The "advanced casus belli" are Imperialism and Nationalism and are gained at diplomatic technology 23. These last as long as the condition is still satisfied.

Casus belli Wargoal Conditions Aggressive expansion modifier Prestige modifier DIP power cost modifier Warscore cost modifier Affected peace offers
Humiliate Rival Take capital
  • Is the country's rival
  • Attacker not revolution target
100% 125% 100% 100%
  • Gold
  • Transfer trade power
  • Annul treaties
  • May Show Strength
  • Can't:
    • Cede province
    • Return core
    • Revoke core
    • Release country
    • Release vassal
    • Force vassalize
Conquest Take target province
  • Defender holds province with attacker's claim
  • Attacker not revolution target
100% 100% 100% 100%
  • Full annexation
  • Cede province
    • Only on provinces attacker has a claim on
Reconquest Take target province
  • Defender holds province with attacker's core
  • Attacker not revolution target
25% 100% 100% 75%
  • Full annexation
  • Cede province
    • Only on provinces attacker has a core on
Independence Defend capital
  • Attacker is a non-colonial subject nation of defender
  • Attacker government form is not Daimyo, or defender government form is not Shogunate
  • Attacker is not revolution target
attacker:
100%
100% 100% 75%
  • Full annexation
    • Allows annexation regardless of total warscore cost
  • Cede province
  • Concede defeat
  • Independence
defender:
50%
  • Full annexation
    • Allows annexation regardless of total warscore cost
  • Cede province
Colonial Independence Defend capital
  • Attacker is a colonial nation of defender
  • Attacker is not revolution target
attacker:
100%
100% 100% 75%
  • Full annexation
    • Allows annexation regardless of total warscore cost
  • Cede province
  • Concession of defeat
  • Independence
defender:
50%
  • Full annexation
    • Allows annexation regardless of total warscore cost
  • Cede province
Nationalism Take target province
  • Attacker is not a subject nation
  • Attacker has diplomatic technology level 23
  • Defender holds a province in attacker's culture group
  • Attacker is not revolution target
50% 150% 50% 50%
  • Full annexation
  • Cede province
    • Only on provinces in attacker's culture group
Imperialism Take capital
  • Attacker is not a subject nation
  • One of:
    • Attacker has diplomatic technology level 23
    • Attacker has Invasion modifier
(only for Jan Mayen in an unmodded game)
  • Attacker is not revolution target
75% 100% 75% 75%
  • Full annexation
  • Cede province
War for the Emperor
Subject Daimyo attacking Japan
Take capital
  • Attacker is a vassal or junior personal union partner of defender
  • Attacker government form is Daimyo
  • Defender government form is Shogunate
  • Attacker is not revolution target
50% 100% 100% 100%
  • Full annexation
    • Allows annexation regardless of total warscore cost
  • Cede province
    • Only on provinces which attacker has a claim on
War for the Emperor
Independent Daimyo Attacking Japan
Take capital
  • Attacker is not a subject country
  • Attacker government form is Daimyo
  • Defender government form is Shogunate
  • Attacker is not revolution target
50% 100% 100% 100%
  • Full annexation
    • Allows annexation regardless of total warscore cost
  • Cede province
    • Only on provinces which attacker has a claim on
Annex Daimyo Take capital
  • Attacker is not a subject country
  • Attacker government form is Shogunate
  • Defender government form is Daimyo
  • Defender owns at least 10 provinces, or is independent
  • Attacker is not revolution target
50% 100% 100% 100%
  • Full annexation
    • Allows annexation regardless of total warscore cost
  • Cede province
    • Only on provinces which attacker has a claim on
Sengoku Take capital
  • Attacker and defender are both subject countries
  • Attacker and defender both have government form Daimyo
  • Attacker neighbors defender
  • Attacker is not revolution target
50% 100% 100% 100%
  • Full annexation
    • Allows annexation regardless of total warscore cost
  • Demand Province
    • Only on provinces which attacker has a claim on
Colonialism Take target colony
  • Attacker or subject neighbors defender's colony
  • Attacker is not revolution target
25% 100% 100% 50%
  • Cede province
    • Only on oversea province attacker (or a subject) borders
Liberation Take capital
  • Not available, only used in historical wars
100% 300% 100% 75%
  • Release vassals
  • Release country
  • Return core
Holy War Superiority
  • Attacker neighbours defender
  • Attacker and defender belong to different religion groups
  • One of:
    • Attacker has Religious idea "Deus Vult"
    • Attacker is Catholic, and the Curia controller has declared a crusade on defender
  • Attacker is not revolution target
75% 125% 100% 100%
  • Cede province
  • Full annexation
Defender of the Faith Defend country
  • Attacker neighbours defender
  • Attacker is Defender of the Faith
  • Attacker and defender belong to different religions
  • Attacker has Religious idea "Deus Vult"
  • Attacker is not revolution target
  • One of:
    • Peace of Westphalia has not occurred (For this to be false requires Art of War to be active, but this is not formally a requirement.)
    • Neither attacker nor defender are members of the Holy Roman Empire
100% 200% 100% 75%
  • Release vassal
  • Release country
  • Return core
  • Revoke core
  • Gold
  • Concession of defeat
Religious Liberation Take target province
  • Only used in historical wars. Seems to be a holdover from EU3.
  • Attacker is not Christian or Muslim
  • Attacker and defender have different religious groups
  • Attacker has Religious idea "Deus Vult"
  • Attacker not revolution target
  • One of:
    • Peace of Westphalia has not occurred (For this to be false requires Art of War to be active, but this is not formally a requirement.)
    • Neither attacker nor defender are members of the Holy Roman Empire
75% 100% 100% 100%
  • Cede province
    • Only on provinces of attacker's religious group
  • Full annexation
Cleansing of Heresy Superiority
  • Attacker neighbors defender
  • Attacker and defender belong to the same religion group
  • Attacker and defender have different religion
  • Attacker has Religious idea "Deus Vult"
  • If Art of War is active and attacker and defender are both in the HRE: the Peace of Westphalia has not occurred
  • Attacker is not revolution target
75% 200% 100% 100%
  • Cede any province
  • Force change religion
Excommunication War Superiority
  • Attacker is Catholic and not excommunicated
  • Defender is Catholic and is excommunicated
  • Attacker neighbors defender
  • Attacker is not revolution target
  • One of:
    • Peace of Westphalia has not occurred For this to be false requires Art of War to be active, but this is not formally a requirement.
    • Neither attacker nor defender are members of the Holy Roman Empire
50% 125% 100% 100%
  • Release vassal
  • Release country
  • Return core
  • Full annexation
  • Cede province
    • Only on province where attacker has claim or core, or neighbors
  • Demand vassalization
  • Demand become protectorate
  • Gold
  • Concession of defeat
Trade Dispute Superiority
  • One of:
    • Defender embargoes attacker, but attacker does not embargo defender
    • Both countries' government form is Merchant Republic
  • Attacker is not revolution target
100% 200% 100% 75%
  • Revoke core
  • Gold
  • Concede defeat
  • Transfer trade power
  • Can't:
    • Full annexation
    • Cede province
    • Return core
    • Revoke core
    • Release vassal
    • Liberate country
    • Force vassalize
    • Force protectorate
    • Form personal union
Imperial Ban Take target province
  • Attacker is Holy Roman Emperor
  • The first imperial reform has been enacted
  • Defender is not in HRE, but holds an HRE province
  • Attacker is not revolution target
100% 125% 100% 75%
  • Release vassal
  • Release country
  • Return core
  • Cede province
    • Only on HRE provinces held by non-HRE country
Coalition Superiority
  • In coalition against defender
  • Defender is not in a coalition war
  • Coalition has at least 3 members
  • Attacker's opinion towards defender is affected by aggressive expansion
  • Attacker is not revolution target
10% 100% 100% 75%
  • Release vassal
  • Release country
  • Return core
  • Revoke core
  • Gold
  • Concession of defeat
  • Cede province
    • Only on province attacker has a core
Claim on Throne Take capital
  • Attacker has a succession claim on defender
  • Attacker is not revolution target
attacker:
100%
200% 100% 140%
  • Form personal union
defender:
50%
100% 75%
  • Cede province
    • Only on province attacker has a core on
Tribal Conquest Superiority
  • Attacker neighbors defender
  • Attacker government form is Steppe Nomad
  • Defender government form is not Steppe Nomad
  • Attacker is not revolution target
  • With Art of War, if a subject has this CB, the overlord can't use it on their behalf.
75% 100% 100% 100%
  • Full annexation
  • Cede province
  • Demand vassalization
  • Demand become protectorate
  • Gold
Tribal Feud Take target province
  • Attacker neighbors defender
  • Both countries' government form is Steppe Nomad
  • Attacker is not revolution target
75% 100% 100% 100%
  • Full annexation
  • Cede province
  • Demand vassalization
  • Demand become protectorate
  • Gold
Revoke Electorate Take target province
  • Common Sense is not active Use "Revoke Electorate" diplomatic action instead.
  • Art of War is not active Apparently it breaks the religious league system.
  • Attacker is Holy Roman Emperor
  • Defender is an elector
  • Attacker and defender have different religion
  • Attacker is not revolution target
100% 200% 100% 75%
  • Revoke elector
Liberate Elector Superiority
  • Attacker is Holy Roman Emperor
  • Defender is an elector
  • Defender has an elector subject
  • Attacker is not revolution target
100% 150% 100% 75%
  • Release vassal
  • Release country
  • Return core
Trade Protection Blockade ports
  • Attacker's home trade node, or one where they have a merchant, where attacker has sufficient power is privateered by defender
  • Attacker is not revolution target
100% 100% 100% 100%
  • Concession of defeat
  • Gold
  • Transfer trade power
    • Costs half amount of warscore
Crush the Revolution Take capital
  • Attacker's capital is in Europe, or attacker neighbours defender
  • Attacker is not a subject
  • Attacker is not revolution target
  • Defender is revolution target
  • Attacker's government form is absolute monarchy, enlightened despotism, despotic monarchy, feudal monarchy, administrative monarchy, constitutional monarchy, or bureaucratic despotism
  • Attacker is not at war with defender
  • Attacker does not have a truce or alliance with defender
  • With Art of War.png, if a subject has this CB, the overlord can't use it on their behalf.
50% 150% 100% 50%
  • Demand vassalization
  • Cede province
  • Revoke core
  • Release vassal
  • Release country
  • Force change religion
  • Gold
  • Concession of defeat
  • Annul treaties
  • (Attacker only) Dismantle revolution

The defender gets an additional +50 war enthusiasm when attacked with this CB.

Spread the Revolution Superiority
  • Attacker is revolution target
  • Defender is not attacker's subject
  • Defender is not a revolutionary republic
  • Defender's capital is in Europe
  • With Art of War.png, if a subject has this CB, the overlord can't use it on their behalf.
50% 150% 100% 50%
  • Demand vassalization
  • Cede province
  • Revoke core
  • Release vassal
  • Release country
  • Force change religion
  • Gold
  • Annul treaties
  • (Defender only) Dismantle revolution
Unify China Show Superiority
  • Attacker's primary culture is not Manchu unless country is Manchu or Qing
  • Attacker's culture group is Chinese
  • Attacker is not a subject nation
  • Defender is not a subject of attacker
  • Defender's culture group is Chinese
  • Defender nation holds lands in the "China Proper" region
  • Defender does NOT hold the Mandate of Heaven
  • Attacker neighbors defender
50% 150% 50% (?) 50%
  • Cede province
    • Only on provinces in the Chinese region
  • Full annexation


Humiliate Take capital
  • Requires Conquest of Paradise.png DLC.
  • Defender is not a subject nation
  • Government form is Native Council
  • Both attacker and defender only own one province
  • Attacker neighbors the defender
  • Attacker not revolution target
0% 0% 100% 0%
  • Humiliate
Religious League Superiority
  • Requires Art of War.png DLC.
  • Neither country is in a league war
  • Defender is Holy Roman Emperor
  • Attacker is league leader
  • Attacker is heretic to HRE
  • Attacker is in opposing league
  • Attacker is not revolution target
50% 150% 100% 50%
  • Demand vassalization
  • Cede province
  • Revoke core
  • Release vassal
  • Release country
  • Force change religion
  • Gold
  • Annul treaties
  • Change HRE religion

The defender gets an additional +50 war enthusiasm when attacked with this CB.

Support Rebels Take capital
  • Requires Art of War.png DLC.
  • Rebel faction that attacker is supporting has risen in revolt against defender
  • Attacker is not revolution target
100% 200% 100% 50%
  • (Attacker only) Enforce rebel demands
Maya Confederation Take target province
  • Requires El Dorado.png DLC.
  • Attacker has Mayan religion
  • Attacker is not a subject nation
  • Attacker has not enacted all religious reforms
  • Defender is not a subject of attacker
  • Defender is in pagan religious group
  • Attacker neighbours defender
75% 125% 100% 100%
  • Cede province
    • Only on provinces of attacker's religious group
  • Full annexation
Flower Wars Take capital
  • Requires El Dorado.png DLC.
  • Attacker's religion is Nahuatl
  • Attacker is not a subject nation
  • Attacker has not reformed the religion
  • Defender is not a subject of attacker
  • Attacker neighbors defender
100% 200% 100% 50%
  • Demand vassalization
  • Demand become protectorate
Force Migration Take capital
  • Requires The Cossacks.png DLC.
  • Defender is migratory nation
100% 100% 100% 100%
  • Force migration

Conquest[edit]

Having a claim allows the selection of the targeted province as a wargoal. The covert Fabricate Claims diplomatic assignment provides a claim on a single province. This is an immediate action that costs a certain number of points of spy network strength, starting at 20 and increasing by 5 spy network points per claim. In addition, many missions, both generic and country-specific, provide temporary claims. Many unification national decisions give permanent claims on a large region. There are also some events, such as Border Friction, that provide claims.

A claim will expire in 25 years after a nation gets the claim (except permanent claims, which never expire). A claim can't expire during a war with the country you have that claim on.

Choosing a CB[edit]

Conquest is ordinarily the easiest CB to get by simply fabricating a claim, but also the least useful. Taking too many provinces can quickly result in a large coalition being formed against the country due to aggressive expansion (AE). It is still desirable to fabricate claims before fighting, in order to reduce coring cost and time, and the diplomatic point cost.

  • Holy War and Cleansing of Heresy work on any heathen or heretic, which also removes diplomatic point cost for taking any province, and are both unlocked by the first Religious idea.
  • Note that a Casus Belli only reduces the cost of provinces that fulfill its criteria. For instance, a Colonialism conquest of <Province> (with that province as the War Goal) has 25% Aggressive Expansion and 50% warscore cost, but only for taking colonies. Provinces on the same continent as the target's capital or directly connected to the capital will incur full costs. When choosing such a CB, it will list the names of all the applying provinces, or show the number of these provinces if there are too many.
  • Also note that the reduced warscore cost also affects options that is set on total province cost. So if a country's warscore cost is just over 100, the reduced cost for being wargoal might just make the country annexable/vassalizable.

If the goal of the war is not to seize territory or force-vassalize, then the choice of CB is less important, since extorting money or releasing nations doesn't cause AE. Conquest is fine to use in such a situation. If the country happens to be a rival and releasing vassals or countries is not desired, the special Humiliate Rival CB is ideally suited for this purpose.

Warfare
Land warfare ArmyLand unitsDisciplineManpower
Naval warfare NavyNaval unitsSailors
Other concepts Casus belliWar exhaustionMilitary traditionLeadersAlliance