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 Triggered casus belli only last for a certain amount of time before they expire and are no longer valid. Without Art of War.png Art of War, none of these CBs can be used by an overlord on a subject's behalf.

Casus belli Wargoal Duration Aggressive expansion modifier Prestige modifier Warscore cost modifier Acquisition Affected peace offers
Restoration of Union Take capital 120 months 100% 100% 100% Given to senior personal union partner when a junior partner becomes independent. Cannot be used by the revolution target.
  • Form personal union
Defected Province Take target province 12 months 100% 200% 50% When a province defects due to rebels
  • Cede province
    • Only on core province defected in last 12 months
Canceled Loan Superiority 12 months 100% 200% 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% 75% Given by two Japanese events involving ninja
  • Revoke core
  • Gold
  • Concede defeat
Disloyal Vassal Take capital 120 months 100% 200% 50% Given to overlord when a vassal breaks free
  • Demand vassalization
Imperial Liberation Take target province 120 months 100% 200% 75% Given to the Emperor when an HRE member state is annexed
  • Cede province
    • Only on HRE provinces with the "Unlawful Territory" province modifier
  • Release vassal
  • Release country
  • Return core
Diplomatic Insult Superiority 12 months 100% 200% 75% By event and the "Send Insult" diplomatic action
  • Revoke core
  • Gold
  • Concede defeat
  • Humiliation
Dishonored Call Superiority 36 months 100% 200% 75% When an ally refuses a call to arms
  • Revoke core
  • Gold
  • Concede defeat
  • Humiliation
Subjugation Take capital 120 months 100% 200% 50% From vassalization missions
Note that some "Subjugate X" missions actually require you to annex them. Pay attention to the mission objectives!
  • Demand vassalization
Obscure Documents Take capital 12 months 100% 100% 150% By event
  • Form personal union
Religious Unity Take capital 24 months 100% 200% 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% 75% Some events
Border friction events generally give claims. One that gives this CB is the "Cossack Aggression" event chain.
  • Cede province
    • Only on neighbouring non-capital provinces
  • Concede defeat
Trade War Superiority 24 months 100% 200% 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 tributary
    • Form personal union
Trade Conflict Blockade ports 24 months 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 tributary
    • Form personal union
Trade Conflict (trade league) Blockade ports 24 months 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
    • Costs half amount of warscore
  • Can't:
    • Full annexation
    • Cede province
    • Return core
    • Revoke core
    • Release vassal
    • Liberate country
    • Force vassalization
    • Force tributary
    • Form personal union
Annexation War Take capital 24 months 50% 100% 100% Given by a few flavour events
  • Full annexation
    • Allows annexation regardless of total warscore cost, but incurs full AE
  • Cede province
    • Only on claimed provinces
Government Form War Take capital 120 months 75% 100% 100% By event (Milan's neighbours when it becomes an Ambrosian Republic)
  • Force change government type
  • Cede province
    • Only on core, claimed, or neighbouring provinces
Forced ally to break alliance Superiority 120 months 100% 200% 75% Given when a Great Power forces an ally to break their alliance with the country.
  • Revoke core
  • Gold
  • Concede defeat
  • Humiliation

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 Warscore cost modifier Affected peace offers
Humiliate Rival Take capital
  • Is the country's rival
  • Attacker not revolution target
100% 125% 100%
  • Revoke core
  • Gold
  • Annul treaties
  • Transfer trade power
  • Humiliate
  • May Show Strength
  • Can't:
    • Full annexation
    • Cede province
    • Return core
    • Release vassal
    • Release country
    • Force vassalize
    • Force tributary
    • Force change religion
    • Concede defeat
    • Revoke electorate
    • Form personal union
Conquest Take target province
  • Defender holds province with attacker's claim
  • Attacker not revolution target

With Art of War.png Art of War, may be used by an overlord on a subject's behalf.

100% 100% 100%
  • Cede province
    • Only on claimed provinces
Reconquest Take target province
  • Defender holds province with attacker's core
  • Attacker not revolution target

With Art of War.png Art of War, may be used by an overlord on a subject's behalf.

25% 100% 75%
  • Cede province
    • Only on provinces attacker has a core on
  • Return core
Independence Defend capital
  • Attacker is a subject nation of defender, other than a colonial nation or tributary
  • Attacker government form is not Daimyo, or defender government form is not Shogunate
  • Attacker is not revolution target
attacker:
100%
100% 75%
  • Concede defeat
  • Independence
defender:
50%
  • Full annexation
    • Allows annexation regardless of total warscore cost, but incurs full AE
  • Cede province
Colonial Independence Defend capital
  • Attacker is a colonial nation of defender
  • Attacker is not revolution target
attacker:
100%
100% 75%
  • Concede defeat
  • Independence
defender:
50%
  • Full annexation
    • Allows annexation regardless of total warscore cost, but incurs full AE
  • Cede province
Nationalism Take target province
  • Attacker is not a subject nation, or is a tributary
  • Attacker has diplomatic technology level 23
  • Defender holds a province in attacker's culture group
  • Attacker is not revolution target
50% 150% 50%
  • Cede province
    • Only on provinces in attacker's culture group
Imperialism Take capital
  • One of:
    • Attacker has diplomatic technology level 23
    • Attacker has Invasion modifier
      (only for Jan Mayen in an unmodded game)
  • Attacker is not a subject nation, or is a tributary
  • Attacker is not revolution target
75% 100% 75%
  • Cede province
War for the Emperor
Subject Daimyo attacking the Shogun
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%
  • Full annexation
    • Allows annexation regardless of total warscore cost, but incurs full AE
  • Cede province
    • Only on claimed provinces
War for the Emperor
Independent Daimyo attacking the Shogun
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%
  • Full annexation
    • Allows annexation regardless of total warscore cost, but incurs full AE
  • Cede province
    • Only on claimed provinces
Annex Daimyo Take capital
  • 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%
  • Full annexation
    • Allows annexation regardless of total warscore cost, but incurs full AE
  • Cede province
    • Only on claimed provinces
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%
  • Full annexation
    • Allows annexation regardless of total warscore cost, but incurs full AE
  • Cede province
    • Only on claimed provinces
Colonialism Take target colony
  • Attacker has a colonial claim against defender. This means:
    • Attacker or their subject colonial nation owns land that is overseas for attacker
    • Defender owns land that is overseas for them or they are a colonial subject
    • These respective provinces neighbour each other
  • Attacker is not revolution target
25% 100% 50%
  • Cede province
    • Only on the provinces that trigger the CB
Liberation Take capital
  • Not available, only used in historical wars
100% 300% 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%
  • Cede province
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% 75%
  • Release vassal
  • Release country
  • Return core
  • Revoke core
  • Gold
  • Concede defeat
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%
  • Force change religion
  • Cede province
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%
  • Release vassal
  • Release country
  • Return core
  • Cede province
    • Only on core, claimed or neighbouring provinces owned by excommunicated Catholics
  • Revoke core
  • Demand vassalization
  • Gold
  • Concede 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% 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
Trade League Dispute Superiority
  • Attacker is leader of a trade league
  • Attacker is not embargoed by defender
  • A member of attacker's trade league is embargoed by defender
  • Attacker is not revolution target
100% 200% 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% 200% 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 already 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% 75%
  • Release vassal
  • Release country
  • Return core
  • Revoke core
  • Gold
  • Concede defeat
  • Cede province
    • Only on core provinces
Claim on Throne Take capital
  • Attacker has a succession claim on defender
  • Attacker is not revolution target
attacker:
100%
200% 140%
  • Form personal union
defender:
50%
100% 75%
  • Cede province
    • Only on core provinces
Tribal Conquest Superiority
  • Attacker neighbors defender
  • Attacker government form is Steppe Nomad
  • Defender government form is not Steppe Nomad
  • Attacker is not revolution target
75% 100% 100%
  • Cede province
  • Demand vassalization
  • Demand tributary
  • Gold
Tribal Feud Take target province
  • Both countries' government form is Steppe Nomad
  • Attacker neighbors defender
  • Attacker is not revolution target
75% 100% 100%
  • Cede province
  • Demand vassalization
  • Demand tributary
  • 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% 75%
  • Revoke electorate
Liberate Elector Superiority
  • Attacker is Holy Roman Emperor
  • Defender has an elector subject
  • Attacker is not revolution target
100% 150% 75%
  • Release vassal
  • Release country
  • Return core
Trade Protection Blockade ports
  • Attacker's home trade node, or one where they have a merchant:
    • Attacker has at least 10% share of trade power
    • Defender's privateers have at least 1% share of trade power
  • Attacker is not revolution target
100% 100% 100%
  • Gold
  • Concede defeat
  • Transfer trade power
    • Costs half amount of warscore
Crush the Revolution Take capital
  • Attacker's capital is in Europe, or attacker neighbours defender
  • The revolution target exists
  • Attacker is not revolution target
  • Attacker is not a subject, or is a tributary
  • Attacker's government form is 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
  • Defender is revolution target
50% 150% 50%
  • Demand vassalization
  • Cede province
  • Revoke core
  • Release vassal
  • Release country
  • Force change religion
  • Gold
  • Concede defeat
  • Annul treaties
  • (Attacker only) Dismantle revolution

Both sides get an additional +50 war enthusiasm when at war with this CB.

Spread the Revolution Superiority
  • Attacker is revolution target
  • Attacker is a player, or attacker's capital is in Europe
  • Defender is not attacker's subject
  • Defender is not a revolutionary republic
50% 150% 50%
  • Demand vassalization
  • Cede province
  • Revoke core
  • Release vassal
  • Release country
  • Force change religion
  • Gold
  • Annul treaties
  • (Defender only) Dismantle revolution
Unify China Superiority
  • Attacker is not a subject nation, or is a tributary
  • Defender is not a subject of attacker
  • If the Mandate of Heaven.png Mandate of Heaven expansion is active:
  • Otherwise:
    • Both countries have a primary culture in Chinese group
    • If attacker's primary culture is Manchu, attacker is Flag of Manchu Manchu or Flag of Qing Qing
    • Defender owns at least one province in North China, Xinan, or South China region
  • Defender does not have the "Mandate of Heaven" country modifier
  • Attacker neighbors defender
50% 150% 50% Attacker:
  • Cede province
    • Only on provinces in the China superregion
Defender:
  • Cede province
    • Only on provinces in the South China, Xinan or South China region or with culture in the same group as defender
Take Mandate of Heaven Take capital
  • The Mandate of Heaven.png Mandate of Heaven expansion is active
  • Attacker is not a subject country
  • Attacker neighbours defender
  • Defender is the Emperor of China
  • Attacker's religion is in pagan or Eastern group
50% 100% 50% Attacker:
  • Cede province
  • Take Mandate of Heaven
Defender:
  • Cede province
Humiliate Take capital
  • The Conquest of Paradise.png Conquest of Paradise expansion is active
  • Attacker's government form is Native Council
  • Attacker does not have a truce with defender
  • Both attacker and defender only own one province
  • Attacker neighbors defender
  • Attacker not revolution target
0% 0% 0%
  • Humiliate
  • Can't:
    • Full annexation
Religious League Superiority
  • The Art of War.png Art of War expansion is active
  • Neither country is already 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% 50%
  • Demand vassalization
  • Cede province
  • Revoke core
  • Release vassal
  • Release country
  • Force change religion
  • Gold
  • Annul treaties
  • Change HRE religion

Both sides get an additional +50 war enthusiasm when at war with this CB.

Support Rebels Take capital
  • The Art of War.png Art of War expansion is active
  • Rebel faction that attacker is supporting has risen in revolt against defender
  • Attacker is not revolution target
100% 200% 50%
  • (Attacker only) Enforce rebel demands
Maya Confederation Take target province
  • The El Dorado.png El Dorado expansion is active
  • Attacker has Mayan religion
  • Attacker is not a subject nation, or is a tributary
  • Attacker has not enacted all religious reforms
  • Defender is not a subject of attacker
  • Defender is in pagan religious group
  • Attacker neighbours defender
75% 100% 75%
  • Cede province
Flower Wars Take capital
  • The El Dorado.png El Dorado expansion is active
  • Attacker's religion is Nahuatl
  • Attacker is not a subject nation, or is a tributary
  • Attacker has not reformed the religion
  • Defender is not a subject of attacker
  • Attacker neighbors defender
100% 200% 50%
  • Demand vassalization
Force Migration Take capital
  • The Cossacks.png The Cossacks expansion is active
  • Attacker neighbors defender
  • Attacker is not a subject nation, or is a tributary
  • Defender is not a subject nation, or is a tributary
  • Defender is migratory nation
100% 100% 100%
  • (Attacker only) Force migration
  • Can't:
    • Full annexation
Force Tributary Take capital
  • Mandate of Heaven.png Mandate of Heaven expansion is active
  • Attacker is Emperor of China
  • Defender is not a subject nation
  • Attacker neighbors defender
50% 200% 50%
  • Force tributary

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 last 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