Casus belli, usually referred to as CB, is a Latin expression literally meaning "case for war". It represents a justification for war that is recognized as legitimate by other nobles, religious leaders or whatever the predominant power structure is. The plural form of casus belli is also casus belli.
As with other games from Paradox Interactive, you need to have a CB to start a war in Crusader Kings II. The CB for the war determines the prize for victory and the price of defeat, as well as frequently determining who can participate in the war and what you need to do to win it.
You can have several CB for a single target, and each has its own goal and reward for success. Some are permanent such as holy wars and de jure claims, and some are only temporary such as excommunication wars. There are several types of CB depending on your religion, your title, and your actions as well as external factors. You are only allowed to push a single CB per war, so you should choose the one that suits your purpose the most.
With the exception of the Tribal Invasion CB all offensive wars incur a one-way 10-year truce for the attacker no matter what the outcome was (unless the war ended inconclusively), and these can be seen on any county personally held by the attacking leader. Truces are between individual leaders, so if the ruler of either the attacking or defending country dies, the truce ends. Breaking this truce will lower general opinion of you of all leaders of that religion (excluding your vassals) and cost 200 + half of your current prestige as well.
 Types of casus belli
Most CB, if one discounts rebellions, are based around claims. If you or one of your vassals or courtiers have a claim upon a title in a realm, you can push this claim through war. If you have multiple personal strong claims upon a single realm you can push all of them at once, but you can only push a single claim for any other character per war. Claims can either be strong or weak. Weak claims can only be pushed if the titleholder is female and the claimant is not, if the titleholder is in regency due to prison, incapability, or youth, or if the title is already being contested.
Upon winning a claim war you, or the person you were pushing the claim for, will gain this title, and if you were pushing it for someone their opinion of you will increase by 100, and you'll gain 100 prestige. If it ends in a stalemate you'll lose 100 prestige, and if it ends in loss, the claim will be lost in addition to 200 prestige. When pushing a vassal's claim and losing you'll have to pay concessions.
Note that if you push a claim that is outside your de jure lands for someone who is not already your vassal or a member of your dynasty, they will not become your vassal upon taking the title. Similarly, if you push someone else's claim for a title equal in rank to your own, they will be independent.
 De Jure
If you or a vassal hold a duchy, kingdom or empire, and part of this land is owned by another realm, you can push a de jure claim upon one of the counties or holdings held by the other realm. Even if the other realm holds more than one county you can only push a single de jure CB at once.
Unlike regular claims, de jure claims cannot be lost unless you lose control of the duchy/kingdom/empire. Losing a war merely means a loss of 200 prestige and a heavy monetary penalty, while you'll still keep the de jure CB.
After winning the war, if the holder of the county is the defender and it's not their only county (including their vassals) you, or the vassal you're pressing the claim for, will get control of the county directly. If it is their only county and they don't have a higher or equal rank title to yours then they will become your vassal (or your vassal's vassal). If it is their only county and they do have an equivalent or higher rank then you will also gain it directly, and they will become unlanded and their higher titles destroyed.
Success also gives 100 prestige, and if you were pushing the de jure claim for someone else they'll have their opinion of you increased by 100, On a white peace, you lose 100 prestige, and the defender gets 50 prestige with a further 50 being divided among the defender and any allies. On a loss, prestige changes are doubled and you also have to pay 4 times your annual income to the defender.
 County claims
Sometimes you or one of your vassals controls a county and one of the minor holdings (barony, temple or city) in the county is held by somebody outside your realm or is independent. (The latter does happen; you can quickly determine if this is the case by both coats of arms on a holding being the same). In this case you will be able to press a county claim in order to gain control of the holding. Prestige gains and losses are half those for a county claim.
 Dispute Succession
If you're a pretender to your liege's throne, or someone in your realm is a pretender to any throne, you can dispute the succession. You are considered a pretender if you were second or third in line to the throne and the old ruler died within the past five years. Upon victory you (or the person you disputed the succession for) will gain the throne, and if it was a kingdom or empire crown authority will be reduced by one. White peace is impossible. If you lose, you'll be imprisoned, lose 200 prestige, and lose the claim.
 For vassals
As long as you're someone's vassal, you can try to achieve independence through war. If your previous liege was themselves the vassal of another liege (for example, if you're a count breaking free from a duke who is in turn under a king), you will become a direct vassal of the higher liege rather than becoming independent.
If you win you'll be free of your current liege, and if the liege you're rebelling from is a king or emperor, crown authority will be lowered one step. If you stalemate you'll lose 100 prestige, and if you lose you'll be imprisoned and lose 200 prestige. Like with changing law, you cannot use this CB more than one step up the chain.
 Depose Liege
As long as no one else is trying to depose your liege, and your liege is not attempting to depose someone else or declaring independence, you can attempt to depose your liege. Upon victory crown authority will be lowered by one step (if the deposed liege is a king or emperor), and your liege will depose to the eligible heir you like the most. If you stalemate you'll lose 100 prestige, and if you lose you'll be imprisoned and lose 200 prestige. Like with changing law, you cannot use this CB more than one step up the chain.
 Faction and Plot CBs
If you are a vassal and meet various prerequisites, you may have some of the following faction or plot options: Claim on Liege Plot, Claim on Vassal Plot, Weaken Vassal Plot, Lower Crown Authority, Change Seniority Succession Law, Change Primogeniture Succession Law, Change Feudal Elective Succession Law, Change Gavelkind Succession Law. Gaining sufficient support will enable you to put the plot into motion - usually resulting in war.
 Religious CBs
 Invasion (Christian)
If you are Catholic and have a claim upon a throne or you're smaller than the realm in question (that is, you have fewer holdings in your realm), and the Pope condones your invasion (costing you 500 piety with Free Investiture or 250 with Papal Investiture), you can use the invasion CB. Upon victory you'll get the throne in question, 400 prestige, and every occupied holding, and also earn the title of "The Conqueror". As such, you should occupy every holding before enforcing demands, as then you can install your own nobles. If you stalemate you'll lose 100 prestige. If you lose you'll lose 200 prestige, and have to pay concessions, and you'll lose your claim upon the throne.
Orthodox and Miaphysite Christians may also use this CB (appealing to the local patriarch rather than the pope), but only if both the ruler and his target are under the authority of the same patriarch. Due to autocephaly, this is rarely the case.
 Invasion (Muslim)
For 500 piety, Muslims may seek to conquer all territory in a de jure kingdom belonging to a ruler of a different religion. Winning grants all holdings held by rulers also owning land outside the kingdom, and also transfers vassalage of all subsidiary lords in the kingdom. The new vassals get a temporary +75 relations modifier with you, making it very easy to demand their conversion. Since patch 1.091, this CB is only usable on kingdoms that you border or own land in.
Main article: Crusades, jihads and great holy wars
This is a special CB only available to religious heads with at least 5% Moral Authority. It targets all territories in a de jure kingdom held by heathens or heretics. Any independent ruler of the same religion can join. Upon success, the participant with the highest contribution gets the kingdom title for the territory as well as all holdings in that territory held by the enemy. If the kingdom title is already held by a ruler of the same religion, that ruler gets the territory instead. In addition, the Moral Authority of the attacker increases by 10% for 20 years, and 500 piety and 1000 prestige are divided among all participants by their percentage contribution, while the loser loses 100 piety and 10% moral authority.
On a white peace, the attacker loses 5% authority and 100 piety while the defender gets 2.5% authority, 200 prestige and 100 piety. On a loss, the attacker loses 10% authority, 200 piety, the principal defender gets 5% authority and 100 piety, and a further 300 prestige and 150 piety is divided up among all defenders.
Christian Crusades are allowed starting in 1090, Muslim Jihads in 1187, and Reformed Pagan Great Holy Wars in 1100.
 Holy War
If you're in a different religious group than your target, your target is a heretic (of your parent religion, so Catholics can't attack Monophysites as they're a Miaphysite heresy), or you are heretic, you can declare a religious war. Muslims can also attack non-heretic Muslims of a different denomination (Shias if Sunni, and vice versa). Upon victory you'll gain 50 prestige and all holdings (as long as they're occupied by you, or unoccupied) in the targeted duchy. If you stalemate you'll lose 50 piety and 100 prestige, and if you lose you'll lose 150 piety, 200 prestige, and be forced to pay concessions. The winner's religion gains 3% moral authority for 20 years and the loser's loses 3%. Since patch 1.091, this CB may only be used on territory bordering yours or within two sea zones of yours.
Note that if you use this CB, neighboring rulers of the defenders faith will be able to (and frequently will) intervene in the war and the defender will be able to summon Holy Orders for only the initial Piety cost. This is best used when neighbors of the target's faith are engaged in other wars and/or the target has low Piety.
Unreformed pagans may not use this CB, but reformed pagans can. The pagan version costs 100 piety on war declaration.
 Excommunicated Ruler
If someone has the same head of religion as you, and has been excommunicated, you can declare war upon them. Victory will give you 10 to 70 piety and 50 to 400 prestige depending on the excommunicated ruler's rank, and the target will be re-communicated and forced to abdicate. A white peace will lose you 50 piety and 100 prestige. Losing will lose you 100 piety, 200 prestige, and you'll be forced to pay concessions.
 County Conquest
Muslims may attack any county bordering their own lands. The CB costs 50 Piety to use, but is usable on any target except your liege. You must have the Piety for the option to show up. Victory gains you the county, or (if the county is ruled by a single-province count) transfers vassalage of the count to you, and gives 100 Prestige. White Peace costs 100 Prestige. Losing costs 100 Prestige and forces you to pay concessions.
 Caliphal Subjugation
Once every 10 years, Muslim caliphs may attempt to subjugate a Muslim de jure kingdom of the same denomination. On success, the target becomes a vassal if he holds no territory outside the kingdom. If he does, all territory within the kingdom is taken.
 Imperial Reconquest
A super-powered CB available only to the restored Roman Empire. On success, subjugates all holdings in the target duchy like in Muslim invasions. May only be used on kingdoms once part of the historical Roman Empire (roughly, all of Europe south and west of the Danube and Rhine, as well as England and the Near East west of Persia). Cannot be used on Muslims, but it does not need to be as Holy War is available for them.
 Seize trade post
For patricians and merchant republics targeting each other. Cannot be used against patricians in the same realm with significantly fewer holdings. On success, you gain the target trade post; on failure, you pay reparations.
 City conquest
A republic-only CB added in patch 1.09. Can be used by patricians as well as doges. Usable if you control a trade post in the province. Targets a single city within the province.
Usable against merchant republics (or their lieges) who control trade posts in your realm. On success, all trade posts are destroyed and you earn significant money for each one conquered in this way.
 Republic county conquest
Republic-only single county conquest, only usable if you already control a city in the province. You must either control a neighboring county or one at most two sea zones away.
 Pagan CBs
 County Conquest
Similar to the Muslim CB, but does not cost piety to use. On success, rewards 50 Piety and Prestige in addition to the county. Only usable on targets of different religion. All pagans may target neighboring counties, and Norse pagans may also target any coastal county if it is held by a non-pagan. Gives 1% moral authority for 20 years on success.
 Tribal Invasion
A modified invasion CB only for Tengri and Aztec Pagans as well as non-Christian Altaic cultures that only requires a neighbor. Any outcome incurs a mere 1-year truce.
Pagans may target all land in a de jure kingdom held by another pagan. On success, all holders are vassalized or conquered, and top-level non-titular titles are seized if they are of equal or higher rank than the invader's top title. Only usable once per lifetime. The "Become King" ambition allows unlimited usage within one's own de jure kingdom.
 Prepared Invasion
Norse Pagans may declare their intent to attack a realm and recruit followers from all over Scandinavia. The target realm must have between 10 and 40 holdings within a de jure kingdom, while the Norse ruler must also have between 10 and 40 holdings as well as 1000 Prestige. During the two years after the invasion is announced, the Norse ruler will receive free troops and ships (scaling with the size of his existing army). Not declaring war within two years cancels the invasion and has a heavy Prestige cost. On success in the war, all holdings within a de jure kingdom are taken. Only usable once per ruler's lifetime.
 Triggered Wars
These CBs cannot be used by the player, but are triggered by events. In each case, a large army appears under the command of a landless leader. On success, the ruler takes all occupied territory, and possibly higher-level titles as well.
Heretic rebels spawn in provinces that follow a heretical religion. They tend to be quite large and seek independence. Nationalist rebels spawn in provinces of a different culture, and seek independence as well as a previously-existing title linked to their culture. Peasant rebels appear in other rebellious provinces. They are generally less powerful than the other rebels, but they too seek independence for their targeted county.
Landless claimants to a title may declare their intention to press their claim and recruit an army. Norse, Frankish and Norman nobles without any claims may also attempt to conquer a coastal duchy. In both cases, assassinating the leader before the war starts stops the invasion. Adventurers have fairly large armies (typically about as big as the total levies of the targeted realm) and are quite dangerous. They automatically receive a treasury of 500 gold. If defeated, they may be banished, netting the ruler all of their money.
 Decadence Invasion
Muslim dynasties with at least 75% decadence may draw the ire of a desert tribe determined to end their corrupt rule. The invasion begins in a random realm province with a very large army appearing. Upon success, the invader gets the top-level titles of the old ruler, as well as getting all occupied holdings. The invader also gets the nickname of "the Conqueror." The Crown Authority of the invaded kingdom is set to Autonomous Vassals. Duke-level or higher vassals will get the option to proclaim their independence from the new authority, although the new invader will get claims on their titles if they do so. On a white peace or failure, the invader is imprisoned by the ruler.
 Rise of the Shia Caliphate
A special targeted invasion that may appear in any Sunni kingdom or empire if no Shia caliph exists. On success, a child leader with the Quick and Sayyid traits takes the kingdom title and becomes the Shia caliph.
 Gaining CBs
While some of these CBs you'll have merely due to your position, like the independence CB and the law change CBs, many of these can be gained on purpose.
First, the easiest type of CB to gain are claims. There are four primary ways to gain claims:
- Forge the claim. This doesn't works for anything above the ducal level (skill of 15 needed to forge a ducal claim)
- Marry someone who has an inheritable claim. Your children will have the claim and you can then push it
- Marry someone in your dynasty to someone who has an inheritable claim. Their children will have the claim, and you'll be able to push it
- Invite someone with a claim to your court. You'll then be able to push it
Second, de jure claims are also relatively easy to gain. If you can create a duchy or kingdom that overlaps another realm's territory, this will gain you a de jure claim, and the same applies if you usurp it. In addition, after pushing a claim for a duchy, you'll often have de jure claims.
Third, dispute succession CBs can, like general claims, be gained by inviting someone with that CB to your realm.
Fourth, excommunication CBs are easy to get as long as the pope likes you, but these won't help you grow your realm. They're good for gaining some prestige, though.
Fifth, you can get religious war CBs on essentially the entire world if you convert to a heresy (A Catholic-derived heretic will have CBs on all rulers except Orthodox and Miaphysite ones or other Catholic-derived heretics, while a Muslim heretic will have CBs on absolutely everyone except other followers of the same heresy). The easiest way to get heresy to appear so that you can convert is appointing an antipope, as this lowers the moral authority of the church. The lower the moral authority of the church, the more likely heresy is to spread. Then upon the first chance you get, you should change to whatever heresy arises. Another option is to have your court chaplain research cultural tech until a heretic find appears. So while the drawbacks of heresy are severe (-30 opinion with all non-heretics, and increased rebel risk), the advantages when it comes to expansion are huge. However, note that it's a two-way street - if you convert to a Catholic heresy then all Catholic rulers get a Holy War CB on you, and the Pope may even declare a Crusade against you.
 Using Your CB
Pushing your own claims and similar is rather straight forward. When pushing someone else's claim however you have to be careful, or they'll end up as an independent realm. They'll only be your vassal if they are already your vassal, they're in your dynasty, or the claim you pushed was for an area that is de jure part of your realm. If the title they took is at the same level as yours or above they'll be independent even if any of the above conditions apply, unless you have a liege above you where the conditions still apply.
The easiest way to ensure that they'll be part of your realm after pushing their claim is granting them a county or barony in your realm first. The only way they can become independent then as a result of the claim pushed, is if the title they gain is at the same tier as yours, or higher.
 Names of wars
You can identify what Casus Belli was used to declare a war by its name. In addition to the examples below, there may be an ordinal prefix indicating that this is the Nth war of that name to have been declared (several may be ongoing at once, e.g. "Byzantine Holy War for Syria" and "2nd Byzantine Holy War for Syria" might be declared at the same time, both targetting the de jure Emirate of Syria, but the parts of it in two different realms).
For some wars, the result is that someone "gains or vassalises" one or more titles. This means that titles that can be vassalised are vassalised, and all the others are gained. Generally a title is gained if vassalising would end up also vassalising a title that wasn't being targetted. For example in the case of a holy war targeting a duchy in which one of the counts had land outside that de jure duchy, the attacker doesn't become their new liege, but just usurps the target titles.
|Name template||Name example||Casus Belli used||Attacker||Defender||Goal (what happens on victory)|
|[Attacker adj](-[Defender adj]) War for ([Claimant]'s claim on]) [Target]||English-Cornish War for David's claim on Devon||Claim (on nearly any title)||The claimant or his liege (i.e. Kingdom of England). If attacker and claimant are the same, the "claimant" part is omitted ("English-Cornish War for Devon" on behalf of the King of England).||The attackable realm (i.e. Duchy of Cornwall) that holds the target title (i.e. County of Devon). If defender and target are the same, the defender isn't mentioned ("English War for David's claim on Devon" attacking the Earl of Devon).||The claimant (i.e. David) gains the target title|
|[Attacker adj]-[Defender adj] De Jure War over [Target]||Welsh-English De Jure War over Devon||De Jure claim||The claimant (e.g. Duchy of Cornwall) or his liege (i.e. Kingdom of Wales), whose de jure but not de facto realm includes the target (i.e. Devon)||The attackable realm that holds the target (i.e. Kingdom of England)||The claimant gains or vassalises the target (i.e. County of Devon)|
|[Attacker adj](-[Defender adj]) Ducal War for ([Claimant]'s claim on) [Target]||Welsh-Somerset Ducal War for Duke David's claim on Devon||? De jure claim on part of the claimant's de jure duchy, where the two sides have the same liege (e.g. Empire of Britannia)||The claimant (i.e. Duke David of Cornwall) or his liege (i.e. Kingdom of Wales). If attacker and claimant are the same, the "claimant" part is omitted ("Cornish-Somerset Ducal War for Devon").||The attackable realm (e.g. Duchy of Somerset) that holds the target title (i.e. County of Devon). If defender and target are the same, the defender isn't mentioned ("Welsh Ducal War for Duke David's claim on Devon").||The claimant gains or vassalises the target.|
|[Attacker adj]-[Defender adj] County War over [Target]||Welsh-English County War over Axminster||County Claim||The holder of the county (i.e. Devon) that controls the target minor holding (i.e. Axminster), or his liege (i.e. Kingdom of Wales)||The attackable realm (i.e. Kingdom of England) that holds the target||The holder of the county containing the target (i.e. Earl of Devon) gains or vassalises the target|
|[Defender adj] Succession Crisis||Welsh Succession Crisis||Dispute Succession||Someone who was a pretender to the target title (i.e. Kingdom of Wales) at the time of the current holder's succession within the last 5 years, or said pretender's liege||Holder of the title being disputed (i.e. Kingdom of Wales)||The claimant usurps the title being disputed|
|War of [Attacker adj] Independence||War of Cornish Independence||Independence (non-faction)||A ruler who is not independent (i.e. County or Duchy of Cornwall)||The attacker's nominal liege (e.g. Kingdom of Wales)||The attacker becomes independent of his nominal liege (as a vassal of his nominal liege's liege, if any, e.g. Empire of Britannia)|
|[Leader adj] League Independence War||Cornish League Independence War||Independence (faction)||All members of the "Independence" faction within the leader's (i.e. the Earl or Duke of Cornwall's) nominal liege's realm (e.g. Kingdom of Wales), led by the leader (i.e. County or Duchy of Cornwall), having had their ultimatum refused||The attackers' nominal liege (e.g. Kingdom of Wales)||All attackers become independent of their nominal liege (as a vassal of their nominal liege's liege, if any, e.g. Empire of Britannia)|
|[Attacker adj] War to depose [Defending ruler]||Cornish War to depose King Hywel I of Wales||Depose Liege||A ruler who is not independent (i.e. County/Duchy of Cornwall)||The attacker's nominal liege (i.e. Kingdom of Wales)||Defender abdicates in favour of his/her heir|
|[Leader adj] War for [Claimant]'s claim on [Target]||Cornish War for Prince Hywel's claim on Wales||Claim on Liege faction||All members of the claim faction (i.e. "Prince Hywel for Wales") in their realm (i.e. Kingdom of Wales), led by the leader (i.e. County or Duchy of Cornwall), having had their ultimatum refused||The faction members' nominal liege (i.e. Kingdom of Wales)||Claimant (i.e. Prince Hywel) usurps the target title (i.e. Kingdom of Wales)|
|[Defender adj] Civil War for [Succession law]||Welsh Civil War for Seniority||Succession law faction||The leader and all members of the succession law faction (i.e. "Seniority Succession in Wales") in their realm (i.e. Kingdom of Wales), having had their ultimatum refused||The faction members' nominal liege (i.e. Kingdom of Wales)||Defender enacts Seniority succession in the target kingdom (i.e. Kingdom of Wales)|
|[Defender adj] Civil war to Lower Crown Authority||Welsh Civil War to Lower Crown Authority||Lower Crown Authority faction||All members of the "Lower Crown Authority" faction in their realm (i.e. Kingdom of Wales)||The faction members' nominal liege (i.e. Kingdom of Wales)||Defender enacts the next lower level of crown authority law in the target kingdom (i.e. Kingdom of Wales)|
|[Attacker] War for a new ruler of [Target].(The plot of [Leader])||Gwyneddian War for a new ruler of Cornwall.(The plot of Dafydd ap Llywelyn)||Weaken Vassal plot||The leader and participants of a plot to weaken a fellow vassal (i.e. "See the Duchy of Cornwall granted to a new ruler") by demanding the target duchy (i.e. Cornwall) be granted to a vassal, having had their ultimatum refused||The holder of the target duchy, whose primary title is another duchy (e.g. Deheubarth)||Defender is forced to grant the target duchy to a vassal?|
|[Attacker adj] Invasion of [Defender]||Cornish Invasion of Wales||Invasion (Christian)||A Christian ruler (i.e. County or Duchy/Petty Kingdom of Cornwall), whose relevant religious head (e.g. pope or ecumenical patriarch) has granted them permission to invade the target||A ruler of the same religion (e.g. both Catholic) as the attacker (i.e. Kingdom of Wales)||Attacker gains all occupied holdings and the target title (i.e. Kingdom of Wales)|
|[Attacker adj] Invasion of [Target]||Abbasid Invasion of Jerusalem||Invasion (Muslim)||A Muslim ruler (i.e. Abbasid Emirate / Sultanate / Empire)||Someone of a different religion who holds land in the target de jure kingdom (i.e. Jerusalem) bordering the attacker's realm, e.g. the Shia Caliph||Attacker gains all occupied territory and gains or vassalises all titles held by the defender in the target de jure kingdom (i.e. Jerusalem)|
|[Religion adj] Crusade/Jihad/Great Holy War for [Target]||Catholic Crusade for Jerusalem||Crusade||Head of the religion (i.e. the pope), joined by other rulers of that religion||A realm (e.g. the Sunni Caliphate) ruled by someone of a different religion holding land in the de jure target kingdom (i.e. Jerusalem)||The participant with the highest contribution, or the existing holder of the target kingdom if the same religion, gains the target kingdom and all titles held by the target in the de jure target kingdom|
|[Attacker] Holy War for [Target]||Welsh Holy War for Cornwall||Holy War||A ruler of any religion other than unreformed pagan (i.e. Kingdom of Wales)||A realm (e.g. Kingdom of England) ruled by someone of a different religion from the attacker (e.g. Norse), holding land in the target de jure duchy (i.e. Cornwall)||The attacker vassalises all rulers of his religion who were vassals of the defender (except ones that have land outside the target, whose titles are usurped instead) and gains all other titles held by the defender within the target de jure duchy|
|[Attacker adj]-[Defender adj] Excommunication War||Gwyneddian-Cornish Excommunication War||Excommunicated ruler||Any Christian realm (i.e. County or Duchy of Gwynedd)||A realm whose ruler is of the same religion as the attacker and is excommunicated (i.e. County/Duchy/Petty Kingdom of Cornwall)||The defender abdicates in favour of his heir|
|[Attacker adj] Conquest of [Target]||Abbasid Conquest of Damascus||Muslim county conquest||A realm ruled by a Muslim (i.e. Abbasid Emirate / Sultanate / Empire)||The realm controlling the target county (i.e. Damascus)||The attacker gains or vassalises the target county|
|[Attacker adj] Subjugation of [Target]||Abbasid Subjugation of Mesopotamia||Caliphal Subjugation||A Muslim Caliphate (or the caliph's liege?)||A realm ruled by someone of the same religion as the attacker holding land in the target de jure kingdom (i.e. Mesopotamia)||The attacker takes or vassalises all titles held by the defender in the target de jure kingdom|
|Imperial Reconquest of [Target]||Imperial Reconquest of Cornwall||Imperial Reconquest||(Restored) Roman Empire||A realm including land within the target de jure duchy (i.e. Cornwall)||The Roman Emperor gains or vassalises all titles held by the defender within the target de jure duchy|
|[Attacker adj]-[Defender adj] Trade War over [Target]||Veglian-Splitian Trade War over Zeta||Seize Trade Post||A patrician or merchant republic (i.e. Veglia)||Another patrician or merchant republic (i.e. Spalato (Split))||The attacker gains the target trade post (i.e. Zeta Trade Post)|
|[Attacker adj]-[Defender adj] War for the City of [Target]||Venetian-Apulian War for the City of Brindisi||Republic city conquest||A merchant republic (i.e. Serene Republic of Venice)||The liege (i.e. Duchy of Apulia) of the target city (i.e. Brindisi), in a county where the attacker controls a trade post||The holder of the trade post gains the target city|
|[Attacker adj]-[Defender adj] War for the Coast of [Target]||Venetian-Croatian War for the Coast of Veglia||Republic county conquest||A patrician or merchant republic, on behalf of himself or his vassal, the mayor of a city (e.g. (i.e.?) Veglia) in a county (i.e. Veglia) that it doesn't control||The realm that controls the county containing the city (i.e. Duchy/Kingdom of Croatia)||The patrician who holds a city in the target county (i.e. Veglia) gains the target county, and his city becomes its capital|
|[Attacker adj] Conquest of [Target]||Scottish Conquest of Northumberland||Pagan county conquest||A pagan realm (i.e. Kingdom of Scotland/Skotland)||The realm containing the target county (i.e. Northumberland)||The attacker gains or vassalises the target county|
|[Attacker adj] Invasion of [Target]||Magyar Invasion of Hungary||Tribal invasion||A Tengri, Aztec or non-Christian Altaic realm (i.e. Kingdom of Magyars)||A realm ruled by someone of a different religion containing land in the target de jure kingdom (i.e. Hungary)||The attacker gains all occupied territory and vassalises territory held by the defender in the target de jure kingdom|
|[Attacker adj] Subjugation of [Target]||Magyar Subjugation of Hungary||Pagan subjugation||A pagan realm (i.e. Kingdom of Magyars)||A realm of the same religion containing land in the target de jure kingdom (i.e. Hungary)||The attacker gains all occupied territory (whether in the target kingdom or not) and takes or vassalises all titles in the target de jure kingdom controlled by the defender|
|[County] Peasant Revolt||Devonian Peasant Revolt||Peasant revolt||[County] Peasant Revolt (a duchy-level titular title held by a peasant leader) (i.e. Devonian Peasant Revolt)||The current top liege of the Earl of Devon||Devon becomes independent, ruled by the peasant leader|
|[Realm] [Heresy] Uprising||Welsh Lollard Uprising||Heretic revolt||[Realm] [Heresy] Uprising (a duchy-level titular title held by a heresiarch, who appears with troops in a county of his religion) (i.e. Welsh Lollard Uprising)||The current top liege of the heresiarch's home county||Devon becomes independent, ruled by the heresiarch|
|[Leader]'s Conquest of [Target]||Sigurðr's Conquest of Cornwall||Adventurer conquest||[Leader]'s Host (a duchy-level titular title) (i.e. Sigurðr's Host)||A realm containing land within the target de jure duchy (i.e. Cornwall)||The attacker gains all the land held by the defender in the target de jure duchy (and the title itself, if it exists within that realm)|
|?||?||Rise of the Sha Caliphate||?||?||?|
Casus belli and claims are easy to gain as long as you know what you're doing. Following these tips you should be able to expand easily.
- All wars except tribal invasions incur a truce which lasts either 10 years or until the death of one of the war leaders.
- Marry claimants with inheritable claims to gain more claims
- Marry your dynasty members to characters with inheritable claims (marry male claimants matrilineally if possible)
- Invite males with inheritable claims and grant them a county
- Invite pretenders and grant them a county
- Make the pope love you and you can farm prestige off of excommunication
- Go heretic and you'll have CBs on everyone
- Create or usurp duchies or kingdoms that overlap the territory of other realms
Additionally, different CBs have different values to you as a ruler. If you have more than one CB, consider pressing them in this order:
- Invasion/Crusade - you gain all land you occupy under the Kingdom title
- Holy War - you gain all heretic/infidel held land in the targeted duchy
- Personal Claim - you can fill up your demesne or select the new holder of the county yourself, can push more than one on a given ruler at a time. Note that you don't get the title's vassals although they become your vassals.
- County Conquest - costs piety can only be pressed one county at a time
- Seize County - you've already got one barony in this county, but this gives you the other 2/3rds of it.
- Dynastic Ducal/County Claim - install a member of your dynasty and add land to your realm.
- Vassal Ducal/County Claim - expands your realm, but the new holder isn't of your dynasty and you're making one of your current vassals more powerful
- Dynastic Kingdom Claim - unless you're an Emperor, this will install a dynastic ally into a Kingdom who can help you in future wars.
- Seize Coastal City - you're only getting one barony-level title out of this.
- Embargo/Excommunication - Great for bringing in money or prestige/piety, but won't expand your realm.