Casus belli
This article is accurate for the latest versions of EU3, Napoleon’s Ambition, In Nomine, Heir to the Throne and Divine Wind.
Casus belli comes from Latin, meaning justification for 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 of war. When declaring war, the player must choose a CB. A proper CB will result in less stability loss and less infamy accumulation compared to the same situation without a CB.
Heir to the Throne
The casus belli system has been completely revamped in the Heir to the Throne expansion pack (HTTT). Instead of just one type of CB, there are several from which the aggressor must choose at the onset of the war. Each CB becomes available in its own way, and each has its own expected War Aims.
No Casus Belli
Declaring war without a casus belli costs -2 stability and gives an immediate +2 Infamy.
Name of War: War of $ATTACKER$ Aggression
Casus belli and alliances
A casus belli only reduces infamy and warscore costs when negotiating with the original target of the war, not with other nations that may join the conflict. For example, if A declared Reconquest on B, and C joined B in defense, A could not take territory at a reduced cost while negotiating with C, even if C owned provinces that were cores of A and was thus itself eligible for the Reconquest casus belli.
For this reason, it is often advisable to simultaneously declare war against multiple countries. In the above example, if A declared separate wars of Reconquest on B and C, each country would be the original target of a casus belli and could thus have taken territory from it at no cost.
Mutual casus belli and defenders
Certain casus belli are mutual, allowing a victorious defender to benefit from the cost reductions of the casus belli. These benefits only apply to eligible provinces. For example, the Reconquest casus belli is mutual, but if A used Reconquest on B, B could only take infamy-free provinces from A if they were cores of B - any other territory would come at full cost.
If the casus belli is not mutual, defenders may take territory at 75% of base cost.
War Aims
Different CBs are designed with different war aims in mind. For example, some CBs may guide the player towards religious conversion or financial reparations. Others, such as the dreaded Excommunication CB, stop nothing short of the total eradication of the target state. While war aims do not by themselves restrict an aggressor's actions in a war, they have a significant impact on the consequences of the war: the eventual peace deal, infamy, and prestige.
Triggered Casus Belli
Some CBs are created by an event, whether by mission or as a consequence of your own actions. These have a duration measured in months.
| Casus belli | Negotiation modifiers | ||||||
|---|---|---|---|---|---|---|---|
| Name | Months | Prerequisites/Trigger | Infamy | Prestige | Warscore | Affected peace options | Name of War |
| Defected province | 12 | A defected province | 0% | 200% | 50% | Demand provinces (only recently defected) | $ATTACKER$ Reconquest of $PROVINCE$ |
| Canceled loan | 12 | A canceled loan | 0% | 200% | 50% | Indemnities, Concede Defeat | $ATTACKER$-$DEFENDER$ War of Recompense |
| Spy discovered | 12 | Discovered spy | 0% | 200% | 50% | Revoke cores, Indemnities, Concede Defeat | $ATTACKER$ War over $DEFENDER$ Provocation |
| Disloyal Vassal | 120 | Vassal breaks vassalization | 0% | 200% | 50% | Become vassal | $ATTACKER$-$DEFENDER$ Vassalization War; |
| Defender of the Faith | 12 | Be Defender of the Faith, Heretic/Heathen state attacks State Religion state | 0% | 200% | 50% | Release vassals, Release annexed, Revoke cores, Reduce sphere, Indemnities, Concede defeat | $ATTACKER_RELIGION$ Defender War |
| Imperial Liberation | 24 | Be Emperor, target owns non-cored HRE provinces | 25% | 200% | 50% | Release annexed, Release vassals, Reduce sphere, Demand provinces (only uncored HRE provinces), Indemnities, Concede defeat | Holy Roman Intervention |
| Guaranteeing Independence | 12 | Violated guarantee | 0% | 200% | 50% | Release vassals, Release annexed, Reduce sphere, Revoke cores, Indemnities, Concede defeat | $ATTACKER$ Intervention |
| Warning | 12 | Violated warning | 0% | 200% | 50% | Release vassals, Release annexed, Revoke cores, Reduce sphere, Indemnities, Concede defeat | $ATTACKER$ Intervention |
| Trade League War | 12 | Be Merchant republic, league member leaves | 0% | 200% | 50% | Join trade league, Indemnities, Concede Defeat | $ATTACKER$-$DEFENDER$ Trade War |
| War of Honor | 12 | Insulted | 0% | 200% | 50% | Revoke cores, Indemnities, Concede defeat | $ATTACKER$-$DEFENDER$ War of Honour |
| Dishonored alliance call | 36 | Alliance member dishonored call to arms | 0% | 200% | 50% | Revoke cores, Indemnities, Concede defeat | $ATTACKER$-$DEFENDER$ War of Honour |
| Restoration of Personal Union | 120 | Broken personal union | 0% | 100% | 100% | Form personal union | $ATTACKER$-$DEFENDER$ Unification War |
| Sphere of Influence | 24 | Sphere of influence violated | 0% | 200% | 50% | Annul treaties, Reduce sphere, Indemnities, Concede defeat | $ATTACKER$ Intervention |
| Subjugation War | 120 | Vassalization mission | 0% | 200% | 50% | Become vassal | $ATTACKER$ Subjugation of $DEFENDER_NAME$ |
| Religious Nonconformist | 24 | HR Emperor, HRE member changes religion | 0% | 200% | 50% | Change religion | Holy Roman-$DEFENDER$ War of Conformance |
| Border friction | 12 | Foreign national focus borders you | 50% | 100% | 50% | Demand provinces (only ones affected by national focus), Concede defeat | $ATTACKER$-$DEFENDER$ Border War |
| Obscure Documents | 12 | Successful fabrication of claim on target's throne | 50% | 200% | 150% | Form personal union | |
Japanese Civil War 
|
12 | Claim title of kampaku | 0% | 150% | 75% | Endorse for shogun, stop endorsing for shogun, become kampaku | Japanese Civil War |
Automatic Casus Belli
Other CBs are created automatically and remain until a certain condition is fulfilled. Peace options generally apply only to certain goals, like a temporary claim or an unowned core province.
| Casus belli | Negotiation modifiers | |||||
|---|---|---|---|---|---|---|
| Name | Prerequisites/Trigger | Infamy | Prestige | Warscore | Affected peace options | Name of War |
| War of Conquest | Temporary claim granted by missions | 25% | 200% | 50% | Annexation, Demand provinces (only mission targets) | $ATTACKER$ Conquest of $PROVINCE$ |
| War of Reconquest | Core province owned by foreign power | 0% | 200% | 50% | Annexation, Demand provinces (only cores) | $ATTACKER$ Reconquest of $PROVINCE$ |
| Call to Arms (also called "Alliance") | Ally under attack with state with which you are at peace and have no truce | 0% | 200% | 50% | Release vassals, Release annexed, Reduce sphere, Revoke cores, Indemnities, Concede defeat | $ATTACKER$ Intervention |
| Nationalism | Government 30, Cultural union state, target owns provinces of your cultural group | 50% | 200% | 50% | Annexation, Demand provinces (only in culture group) | $ATTACKER$-$DEFENDER$ Nationalist War |
| Imperialism | Revolutionary Empire, Revolutionary Republic, Enlightened Despotism, Republican Dictatorship, Absolute Monarchy | 50% | 100% | 75% | Annexation, Demand provinces (any) | $ATTACKER$-$DEFENDER$ Imperialist War |
| Revolutionary War | Revolution and Counterrevolution NI and one of these must be true: republic government and monarchic target, monarchial government and republican target | 25% | 100% | 50% | Annexation, Demand provinces (any) | $ATTACKER$-$DEFENDER$ Revolutionary War |
| Colonial War | Quest for the New World NI, Colony Claim, Overseas Provinces | 25% | 100% | 50% | Demand provinces (only neighboring overseas) | $ATTACKER$-$DEFENDER$ Colonial War |
| Liberation War | Bill of Rights NI, Target can release vassals | 0% | 300% | 50% | Release vassals, Release annexed, Reduce sphere | $ATTACKER$-$DEFENDER$ Liberation War |
| Holy War | Before 1650, Christian or Muslim, target is of different religious group and one of these must be true: Be an Empire, Defender of the Faith, border target, be Catholic and target has Crusade called against it, Unam Sanctum NI, Divine Supremacy NI. | 25% | 150% | 50% | Annexation, Demand provinces (any) | $ATTACKER$ Crusade/Jihad against $DEFENDER_NAME$ |
| Religious Liberation | Not Christian or Muslim, target is of different religious group, target owns a province from your religion group and one of the following must be true: Be an Empire, Defender of the Faith, border target, Unam Sanctum NI, Divine Supremacy NI | 25% | 125% | 100% | Annexation, demand provinces (same religious group) | $ATTACKER$-$DEFFENDER$ Religious War |
| Purging of Heresy | Unam Sanctum NI, Must Be In Same Religious Group, and one of these must be true: Have the "Heretic Country" Flag, Target have "Heretic Country" Flag, Target have different religion | 50% | 200% | 50% | Change religion, Demand provinces (any) | $ATTACKER$ Purge of $DEFENDER$ Heresy |
| Excommunication War | Before 1650, Be Catholic, Target is Excommunicated | 25% | 125% | 50% | Release vassals, Release annexed, Annexation, Demand provinces (only provinces in same culture group as your nation!), Revoke cores, Become vassal, Reduce sphere, Indemnities, Concede defeat | $ATTACKER$-$DEFENDER$ Excommunication War |
| Trade War | Embargoed, Merchant Republics get CB on each other | 0% | 200% | 50% | Join trade league, Revoke cores, Indemnities, Concede defeat | $ATTACKER$-$DEFENDER$ Trade War |
| Imperial Ban | Emperor, Reichsreform passed, enemy capital outside HRE | 10% | 200% | 50% | Release vassals, Release annexed, Demand provinces (only in HRE), Reduce sphere | Holy Roman Reclamation of $PROVINCE$ |
| Dishonorable Scum (Badboy Wars) | Infamy limit surpassed | 25% | 100% | 75% | Release vassals, Release annexed, Annexation, Demand provinces (any), Revoke cores, Reduce sphere, Indemnities, Concede defeat | $ATTACKER$-$DEFENDER$ Punitive War |
| War on Pagans | Pagan target, not be a Pagan | 20% | 100% | 50% | Annexation, Demand provinces (any), Revoke cores, Release vassals, Release annexed, Reduce sphere, Indemnities | $ATTACKER$ Conquest of $DEFENDER_NAME$ |
| Claim Throne | Succession claim | 10% | 200% | 100% | Form personal union, Annexation | $ATTACKER$ War for the $DEFENDER_NAME$ Throne |
| Tribal conquest (in cb_types.txt under 'Horde vs Civilized') | Either attacker has Tribal Despotism, Tribal Federation, or Tribal Democracy government and target is non-Tribal, or attacker is non-Tribal and target has Tribal Despotism, Tribal Federation, or Tribal Democracy government | 50% | 100% | 100% | Annexation, Change religion, Indemnities, Become vassal | $ATTACKER$ Conquest of $DEFENDER_NAME$ |
4.1 Beta
The 4.1 Beta has introduced two new Casus Belli in HTTT: "Tribal Feud" and "Horde".
| Casus belli | Negotiation modifiers | |||||
|---|---|---|---|---|---|---|
| Name | Prerequisites/Trigger | Infamy | Prestige | Warscore | Affected peace options | Name of War |
| Tribal Feud | Attacker borders Tribal target and have Tribal Despotism or Tribal Federation government | 25% | 100% | 100% | Indemnities, Annexation, Demand provinces (any), Become vassal, Change Religion | $ATTACKER$ Conquest of $DEFENDER_NAME$ |
| Horde | One of these must be true: Attacker borders non-Tribal target and have Tribal Despotism or Tribal Federation government, Attacker borders a government with Tribal Despotism or Tribal Federation government and is not Tribal | 50% | 100% | 100% | Indemnities, Annexation, Demand provinces (any), Become vassal, Change Religion | $ATTACKER$ Conquest of $DEFENDER_NAME$ |
See also
In Nomine
You can get casus belli (plural) in several ways:
- If another country owns a province your nation considers one of its cores, you have a CB against that nation. Be aware that core claims go away after a good time. It happens when you lose a core on that province, usually after 50 years or as a consequence of a certain peace resolution. A flag shows up when the CB is about to end.
- Sometimes an event might pop up giving a CB (a diplomatic incident or a Boundary Dispute). But be careful - you take a huge prestige hit (25 points) any time a core in another land expires. Thus you should only Press The Issue unless you plan to take that province within 50 years. Cores in provinces with your culture, however, never expire. A Diplomatic Insult event gives a temporary Casus Belli that expires within a year from the date received.
- Should you warn a country and it still goes to war with one of its neighbours you will also gain a CB. (In In Nomine, you get a call to war as if you were an ally of the country attacked)
- If you are the Emperor of the Holy Roman Empire, then you gain a casus belli on anyone attacking any member of the Empire. (In In Nomine, you get a call to war as if you were an ally of the member attacked. Refusing to defend the Empire seriously damages your chances of being re - elected as Emperor.)
- If you have Unam Sanctum national idea you have a casus belli on anybody in your religion group who doesn't share your religion. Other countries do not respect this casus belli, however, so you still suffer the full reputation penalty for declaring aggressive war.
- If you insult a country, it gets a CB against you.
- When your ally is attacked by somebody or attacks somebody you have a casus belli on that country. (In In Nomine, you will automatically be asked to join the war of any ally that gets attacked. Refusing to join in the defense of your ally dissolves the alliance and gives them a casus belli against you.)
- If you send a spy to a capital city, you can fabricate claims on their country. If the spy is successful, you gain a casus belli on that country for a year.
- If you have a royal marriage, you can try to claim their throne. You gain a CB on that nation but suffer a penalty in relations with every other nation you have royal ties with, but you still suffer the -1 Stability hit for attacking Royal Relatives.
- If you offer a loan to a country and the country does not pay the loan you will be given an casus belli. However many players believe that the loan offer is an exploitative casus belli because countries rarely repay the loan .
There are some changes to how religions influence CBs in In Nomine:
- For the early part of your game you essentially have a free CB against all infidels—that is, a Catholic nation could attack a Muslim one with neither a stab hit nor a BB penalty. The war would still be titled the nth war of [Country] Aggression, though.
- This bonus goes away after the end of the counter reformation, in the mid 17th century
- The Unam Sanctum NI is much less valuable early game for this reason, but still seems to provide a partial amelioration of penalties when attacking heretics (e.g., Protestant versus Catholic)
Military:
Leaders • Maintenance • Morale • Manpower • Ship types (Big ship • Light ship • Galley • Transport) • Land unit types (Infantry • Cavalry • Artillery)
Warfare:
Assault • Basic Warfare • Casus Belli • Combat • Making peace • Siege • Supply & attrition • War Capacity • War Exhaustion
