Casus belli

A casus belli, sometimes abbreviated CB and meaning "Cause for War" in Latin, represents a justification for war that is recognized as legitimate by other characters. A ruler must have a valid casus belli in order to be able to declare war upon another ruler and can only gain from a war what the casus belli specifies.

Objective

The Objective is the map region which is targeted by a casus belli. If the casus belli does not target a map region then the defender's Realm Capital becomes the Objective.

The attacking side gains more War Score by occupying Holdings located in the Objective region. After a grace period, the defender will passively gain War Score by holding all Counties in the Objective region.

Casus belli list

Each casus belli will cost Prestige and/or Piety. If a character cannot pay the cost, then they can pay with a Level of Prestige or Level of Devotion instead. Declaring war against a character's Head of Faith costs 500 Piety if the Head of Faith is Spiritual and 100 Piety if Head of Faith is Temporal.

Casus belli costs can be removed via one of the game rules.

General CBs

Casus belli	Requirements	Cost	Enforce Demands effect	White Peace effect	Surrender effect
Independence War	Target is the liege	500 Prestige if not tribal 250 Prestige if tribal	Attacker becomes independent	Attacker stays a vassal	Attacker stays a vassal Defender imprisons the attacker Defender gains title revocation reason
Seize De Jure County	Tribal-era innovation Casus Belli 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	Early Medieval-era innovation Chronicle Writing De jure title above target duchy	100 prestige per county	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	Late Medieval-era innovation Rightful Ownership De jure titles above targets	100 prestige per county	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 High Medieval-era innovation Divine Right Pressing several of another's claims at once requires the Late Medieval-era innovation Rightful Ownership	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)	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: Tribal government Eastern religion Temporal head of faith	1000 prestige if not tribal 500 prestige if tribal	Attacker vassalizes the defender	Defender stays independent	Defender stays independent Attacker's factions gain discontent
Raid for Captives	Faith has the Human Sacrifice tenet	80 if faith has the Armed Pilgrimages tenet 100 otherwise	Attacker imprisons 3–5 of the defender's courtiers	Attacker gains no prisoners	Attacker gains no prisoners
Excommunication War	Same faith as defender and any liege(s), and that faith allows excommunication Target is independent Target 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 keeps 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: Casus Belli (Tribal era) Chronicle Writing (Early Medieval era) Divine Right (High Medieval era) Rightful Ownership (Late Medieval era) 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 feudal and same faith 50 piety if 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 vassalizes all rulers in target empire within defender's realm whose religion is more tolerated by attacker than defender's, and 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 CBs

The following CBs are only available to rulers who have clan or tribal government or whose 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 by white peace, the defender keeps the target title and the attacker loses 75 prestige.
If the war ends by surrender, the defender's keeps the target title and the attacker must pay gold and gain +25 faction discontent.

Objective rank	Required level of fame	Same faith cost	Different faith cost	War contribution share
County	Established	50 if character has tribal government 100 if character has clan government	75 if character has tribal government 150 if character has clan government	75
Duchy	Illustrious	250 if character has tribal government 500 if character has clan government	375 if character has tribal government 750 if character has clan government	150
Kingdom	Exalted Among Men	2000	2000	350

Holy War CBs

The following CBs will cause a holy war instead of a regular one. They require the faith to be organized and to not have the Pacifism or Dharmic Pacifism tenets, and can only target rulers whose faith is considered hostile or evil.

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 gold and gain +25 faction discontent and −15 vassal opinion for 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
County	Dutiful	3	100	80	100
Duchy	Faithful	5	200	160	200
Kingdom	Paragon of Virtue	10	750	600	500

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 Kingdom of Hungary title, which replaces Kingdom of Pannonia
Any other kingdom title held by the attacker is destroyed
Any held title that is not within the de jure realm of Kingdom of Hungary is given to another character
All vassals that are not within the de jure realm of Kingdom of Hungary 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:

Years	Levies	Horse Archers
867-889	3000	2000
890-904	5000	3000
905+	6000	4000