Casus Belli
Casus Belli is a Latin expression meaning “an act or event that provokes or is used to justify war”. In Crusader Kings III it is the required to declare War on another Ruler. There are a number of different ways to obtain Casus Belli for your wars and the Casus Belli specifies what the War is about, usually a specific War Target. It is important to note that whatever Casus Belli you choose as your War Target you will not gain anything more than the Casus Belli Claims you or an opposing ruler chose to start the War, regardless of how soundly the enemy is defeated.
One of the most important Casus Bellis are Claims, or legal rights to a Title, whether they are from Succession or the Fabricate Claim on County Task. Below are examples of the different options of Casus Belli from the Declare War screen.
Objective
Depending on which Casus Belli chosen for Declaring War there will be an objective associated with winning your war and contributes to the War Score. If the Casus Bellie does not target a map region then the defender’s Realm Capital becomes the objective.
Both sides will start at 0% of the War Score and it will change over time either positively or negatively until there is a conclusion to the War. Both sides will gain War Score by; Controlling the Target Objective (County, Duchy, etc.), Occupying Holdings, Winning Battles, and Capturing Key Enemy Combatants such as Rulers or Heirs.
Casus Belli List
Every Casus Belli will cost either Prestige and/or Piety. If the Ruler cannot afford the cost, then they can pay with a Level of Fame (Prestige) or Level of Devotion (Piety) instead.
Notes:
- Presitge De Jure claims require certain Innovations
- Characters’ Claims may not be valid Casus Belli, depending on the Faith’s view on gender.
- For Faiths with Male Dominated doctrine, female characters’ Claims may not be used to seize titles from male titleholders, unless the targeted ruler is a child or has the incapable trait.
- For Faiths with Female Dominated doctrine, male characters’ Claims may not be used to seize titles from female titleholders, unless the targeted ruler is a child or has the incapable trait.
- Casus Belli costs can be removed via one of the games rules upon start up of a new game. Just keep in mind that you will not be able to earn achievements if you alter the rules and don’t have ironman mode enabled.
| Casus Belli | Requirements | Cost | Enforce Demands Effect | White Peace Effect | Surrender Effect |
|---|---|---|---|---|---|
| Independence War | Target is the liege | 500 Prestige if not tribal | Attacker becomes independent | Attacker stays a vassal | Attacker stays a Vassal |
| 250 Prestige if tribal | Defender imprsons the attacker | ||||
| Defender gains title revocation reason | |||||
| Seize De Jure County | Casus Belli Innoviation (Tribal era) De Jure Title above target county | 100 Prestige | - The De Jure Liege in attacker's realm gains the targeted county - If that character is not attacker, attacker gets a weak hook (Favor) on them | Defender keeps their titles | - Defender keeps their titles - Attacker pays war reparations |
| Seize De Jure Duchy | - Chronicle Writing Innovation (Early Medieval era) - De Jure titles above targets | 100 Prestige | - The De Jure Liege in attacker's realm gains the targeted county - If that character is not attacker, attacker gets a weak hook (Favor) on them | Defender keeps their titles | - Defender keeps their titles - Attacker pays war reparations |
| Seize De Jure Titles | - Rightful Ownership Innovation (Late Medieval era) - De Jure Titles above targets | 100 Prestige | - All titles that are de jure vassals of characters in attacker's realm are gained by those characters - Attacker gets a weak hook (Favor) on each vassal who gains a title this way | Defender keeps their titles | - Defender keeps their titles - Attacker pays war reparations |
| Claims | - Claim on the target - Pressing several of one's own claims at once requires the Divine Right innovation (High Medieval era) - Pressing several of another's claims at once requires the Rightful Ownership innovation (Late Medieval era) | - 100 Prestige per County (own claim) - 200 Prestige per Duchy (own claim) - 400 Prestige per Kingdom (own claim) - 800 Prestige per Empire (own claim) - 250 Prestige per County (other's claim) - 500 Prestige per Duchy (other's claim) - 1000 Prestige per Kingdom (other's claim) - 3000 Prestige per Empire (other's claim) - 125 Prestige if claimant is of different dynasty | - Claimant gains the targeted titles - Attacker gets a weak hook (Favor) on any other character who gained titles | Defender keeps their titles | - Defender keeps their titles - Claimant loses the claims used |
| Subjugate | One of the following are required: - Tribal government - Eastern religion - Temporal Head of Faith | - 1000 Prestige if not tribal - 500 Prestige if tribal | Attacker vassalizs the defender | Defender stays independent | - Defender stays independent - Attacker's factions gain discontent |
| Raid for Captives | Faith has the Human Sacrifice Tenet | - 80 Piety if faith has the Armed Piligrimages tenet - 100 Piety otherwise - if both attacker and defender follow the same faith, they will both receive Piety regardless of the outcome (less for the loser) | Attacker imprisons 3-5 of the defender's courtiers | Attacker gains no prisoners | - Attacker gains no priosners - if defender also follows a faith that has the Human Sacrifice tenet, defender imprisons 3-5 of the attacker's courtiers |
| Excommunication War | - Same faith as defender and any liege(s), and that faith allows excomunication - Target is independent - Targe has the Excommunicated trait | None | Defender is deposed (i.e. succession happens as though the character had died) | Defender keeps their titles | - Defender keeps their titles - Defender loses the Excommunicated trait - Attacker loses Opinion with Head of Faith |
| Ducal Conquest of County | - Ducal Conquest lifestyle perk (Diplomat tree) - Attacker owns a County in the same uncreated Duchy as the target County | - 350 Prestige if target's title rank is Count - 750 Prestige if target's title rank is higher than Count | Attacker gains the target County | Defender keeps their titles | - Defender keep their titles - Attacker's factions gain discontent |
| Forced Vassalization | - Forced Vassalage lifestyle perk (Diplomat tree) - Defender is an independent neighbouring realm with no more than 3 counties, plus 2 for each of the following Innovations: - Caus Belli (Tribal era) - Chronicle Writing (Early Medieval era) - Divine Right (High Medieval era) - Righful Ownership (Late Medieval era) - X Defender is not a holy order or attacker's Head of Faith | 125 Prestige per County | Attacker vassalizes the defender | Defender stays independent | - Defender stays independent - Attacker's factions gain discontent |
| Laudably Conquer County | - Request Claim on Ireland Decision - Attacker and defender don't have the same top Liege - Target County is in the Hibernia region | - 150 Prestige if feudal and different faith - 75 Prestige if tribal and different faith - 100 Piety if fedual and same faith - 50 Piety fi tribal and same faith | Attacker gains the defender's titles | Defender keeps their titles | - Defender keeps their titles - Attacker's factions gain discontent |
| Mongol Invasion of Empire | - Mongol Empire title - Tribal government - Fame level is Established or higher - Target title is adjacent to attacker's realm | 200 Prestige | Attacker vasslizes all rulers in target Empire within defender's realm whose religion is more tolerated by attacker than defender's, ad gains all other counties | Defender keeps their titles | - Defender keeps their titles - Attacker's factions gain discontent |
| Restore Imperial Province | - Roman Empire Title - Duchy was part of the Roman Empire - Religion is Christian or Greco-Roman | None | Attacker gains all land in the target duchy within defender's realm | Defender keeps their titles | - Defender keeps their titles - Attacker must pay war reparations |
Conquest Casus Bellis
There are additional Casus Bellis available to rulers who either have clan or tribal government, an unreformed faith, or their faith has the Warmonger or Pursuit of Power tenets.
- If the war ends by enforcing demands, the attacker will gain the target title and fame equal to the war contribution share.
- If the war ends in white peace, the defender keeps the target title and the attacker loses 75 Prestige.
- If the war ends by surrender, the defender keeps the target title and the attacker must pay gold in war reparations and gains +25 faction discontent.
| Objective Rank | Required Level of Fame | Same Faith Cost | Different Faith Cost | War Contribution Share | Once Per Lifetime? |
|---|---|---|---|---|---|
| County | Established | - 50 Piety if character has tribal governement - 100 Piety if character has clan government | - 75 Prestige if character has tribal government - 150 Prestige if character has clan government | 75 | No |
| Duchy | Illustrious | - 250 Piety if character has tribal governement - 500 Piety if character has clan government | - 375 Prestige if character has tribal government - 750 Prestige if character has clan government | 150 | No |
| Kingdom | Exalted Among Men | 2000 Piety | 2000 Prestige | 350 | Yes |
Holy War Casus Bellis
The following Casus Bellis will cause a holy war instead of a regular war. They require the faith to be organized and to not have the Pacificsm or Dharmic Pacifism tenets, and can only target rulers whose faith is considered hostile or evil. Vassals may only declare holy wars if they are of the same faith as their liege.
- If the war ends by enforcing demands, the attacker will gain all titles held by rulers of different faith and vassalize all rulers of the same faith in the target region.
- If the war ends by white peace, then the defender keeps all their titles and the attacker loses 50 Piety.
- If the war ends by surrender, then the defender keeps all their titles, its faith gains fervor equal to the attacker’s cost, and the attacker must pay war reparations of gold to the defender and gains +25 faction discontent and -15 vassal opinion for the next 5 years.
| Objective Rank | Required Level of Devotion | Fervor Cost | Piety Cost (without Armed Pilgrimages tenet) | Piety Cost (with Armed Pilgrimages tenet) | War Contribution Share | Once Per Lifetime |
|---|---|---|---|---|---|---|
| County | Dutiful | 1 | 100 | 80 | 100 | No |
| Duchy | Faithful | 2 | 200 | 160 | 200 | No |
| Kingdom | Paragon of Virtue | 5 | 750 | 600 | 500 | Yes |
Migrate to Pannonia
Migrate to Pannonia is a unique casus belli with special mechanics that can only be used once per game by characters of Táltosist faith who make the Prepare to Cross the Carpathians decision against characters in the Pannonian Basin region. If the Hungarian Migration game rule is set to Immediate the game will start with the casus belli being used by Grand Prince Álmos Ügyekfi of the Mogyër Confederation against King Boris of Bulgaria.
If the war ends in white peace, the defender keeps his or her titles. If it ends in surrender, the attacker’s factions will also gain discontent. If the war ends by enforcing demands however it will have the following effects:
- Attacker gains all titles held by the defender in the Pannonian Basin region
- Attacker gains the Grand Principality of Pannonia title, and any Principality titles with de jure capitals in the captured territory.
- Any other kingdom title held by the attacker is destroyed
- Any held title that is not within the de jure realm of Grand Principality of Pannonia is given to another character
- All vassals that are not within the de jure realm of Grand Principality of Pannonia become independent
- All controlled counties convert to Mogyër culture and Táltosist faith.
- All previously controlled counties convert to Pecheneg culture.
When the Casus Belli is used it will spawn the following army for as long as the attacking character lives:
- 3000 Levies & 2000 Horse Archers from Years 867-889
- 5000 Levies & 3000 Horse Archers from Years 890-904
- 6000 Levies & 4000 Horse Archers from Years 905-910