政府
政府（government）とはキャラクターと土地を支配する制度のことです。Crusader Kings IIIには、さまざまな政府のタイプや政体があります。これによりキャラクターが使用できる法律（laws）と、封臣（vassal）が主君（liege）に対して負う義務(税金と徴募兵)が決まります。プレイ可能な政府政体が三つあり(封建制（feuda）、部族制（tribal）、クラン制（clan）)、プレイ不可能な政府政体が二つあります(神権制（theocracy）と共和制（republic）)。
封建制
封建制政府（Feudal governments）は新たな領地（holdings）や分家（cadet branches）を作ることができます。また、
王権（Crown Authority）も利用することができます。封建制の封臣はそれぞれ封建契約を持っており、それは一生に一度だけ変更することができます。またそれは法的義務（obligations）と特権を持つかどうかを決定します。
法的義務
各封臣の封建契約によって 法的義務（obligations）が決まり、それは一度に一段階ずつしか変更できません。法的義務はいつでも引き下げることができますが、それを引き上げることは、他の法的義務を引き下げるか、封臣に権利（right）を与えない限り、+20の暴政（tyranny）をあなたに追加することになります。主君は暴政を避けるために封臣にフックを使用することもできます。
キャラクターが封臣の「正当な君主（rightful liege）」でなかった場合、法的義務は軽減されることがあります。デフォルトではこれは50%です。主君が封臣の2ランク上の慣習的領土（de jure）の称号を保持している場合(一例を上げれば伯爵に対する王)、これは25%になります。正当な君主になるためには、キャラクターが封臣の主要称号（primary title）の慣習的領土の称号を直接、所有していなければなりません。主君が慣習的領土の称号を所有しているような公爵（Dukes）は、このペナルティを免除されます。
| 法的義務のタイプ | 免除の効果 | 法律の効果 | 通常の効果 | 高い効果 | かなり高い効果 |
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 税金
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 徴募兵
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権利
権利（Rights）は
封臣に、彼らがデフォルトでできないことを許可（permissions）するものです。権利は、暴政（tyranny）を避けて法的義務（obligation）を増やそうとする場合に追加できます。権利を撤回することは、他の権利を代わりにしない限り、暴政を招くでしょう。
| 権利 | 主君の効果 | 封臣の効果 | 要求事項 |
|---|---|---|---|
| 貨幣権（Coinage Rights）: 授与（Granted） |
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貨幣制度の革新性（innovation） |
| 評議会強制参加権（Council Rights）: 保証（Guaranteed） |
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| 要塞化の利権（Fortification Rights）: 授与 |
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胸壁（Battlements）の革新性 |
| 宗教的な権利（Religious Rights）: 保証されている（Protected） |
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封臣は主君の宗派ではない |
| 相続の権利（Succession Rights）: 分割相続の強制（Forced Partition） |
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| 称号の剥奪（Title Revocation）: 剥奪不可（Protected） |
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| 宣戦布告（War Declaration）: 許可（Sanctioned） |
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特別な契約
特別な契約（Special contracts）は封臣のなかでも公爵と王にのみが利用でき、一定の革新性を必要とします。いずれの特別な契約も封臣に追加のボーナスを与えます。
| 特別な契約 | 主君の効果 | 封臣の効果 | 必要とされる革新性 |
|---|---|---|---|
| 軍役免除税（Scutage） |
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−20% 常備軍の維持費
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 軍役代納金（Scutage）
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| 辺境伯（March） | −50% 封臣からの税金
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 ブルス（Burhs）
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| 宮中伯（Palatinate） |
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 神権（Divine Right）
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Clan
Clan governments can create new holdings and cadet branches and have access to the crown authority law; just like feudal governments, innovations are required to unlock higher crown authority. They also have access to the Conquest casus belli, which can be used once in a lifetime to invade a realm, with higher-rank realms allowed at higher levels of fame.
Clan vassals provide taxes and levies based on their opinion of their liege. There is always a minimum of taxes and levies they will provide, which is determined by the liege's crown authority law. All vassals will want to be in an Alliance with their liege and will gain -15 
Opinion of their liege if they are not. The penalty is doubled for Powerful Vassals.
If a clan ruler is a Dynasty Head, their realm will be named after their dynasty rather than the primary title.
Taxes and levies contribution
By default, a clan vassal will provide 15% of their taxes to their liege, and 30% of their levies. This amount is then adjusted with the vassal's opinion of their liege.
Scaling contribution
For every point of opinion above 0, a clan vassal will provide an additional 0.1% taxes and 0.305% levies, for a maximum of +10% taxes and +30.5% levies at 100 opinion.
For every point of opinion below 0, a clan vassal will subtract 0.3% taxes and 0.4% levies from their obligations, meaning that at −50 Opinion of their liege, a clan vassal will provide no taxes, and that at −75 opinion of their liege, a clan vassal will provide no levies.
The following table gives a quick recap of a vassal contribution to their liege, taking their opinion of said liege into account.
| Opinion of their liege | −100 | −50 | 0 | 50 | 100 |
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| Taxes
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| Levies
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Minimum contribution
The minimum amount of taxes and levies provided by a clan vassal is dictated by the liege's crown authority law. The following table gives the minimum contribution of a lord's vassals, depending on the lord's crown authority law.
The "Opinion of their liege" line corresponds to the opinion needed by a clan vassal to be provided the same amount of taxes or levies. A vassal having a worse opinion of their liege would not affect their contributions to their suzerain.
| Crown authority | Autonomous vassals | Limited crown authority | High crown authority | Absolute crown authority |
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| Minimum levies
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Player vassal
If the clan vassal is a human player, then they will always contribute 10% of their taxes and 25% of their levies to their liege. This amount is flat, and will not be adjusted by the player character's opinion of their liege. This is roughly equivalent to a clan vassal having −15 opinion of their suzerain.
Tribal
Unlike feudal or clan governments, tribal governments have access to the Tribal Authority law, and can raise it without having to research innovations. If tribal authority is high enough, a tribal ruler can reform their government to become feudal or clan. They also have access to the Conquest casus belli, which can be used to invade a realm, with higher-rank realms allowed at higher levels of fame.
Tribal governments have the following unique effects:
- Holdings cannot be created in counties ruled by a tribal ruler, even by a clan or feudal liege.
- Development will only affect supply limit, as tax and levy development increase does not apply in counties ruled by a tribal ruler. (However, a certain level of development is needed to reform government.)
- Development does not passively grow in counties ruled by a tribal ruler.
- Tribal baronies only provide half of their supply limit to armies belonging to other governments.
- Tribal rulers can only discover Tribal-era innovations.
- For succession, tribal rulers are locked to Confederate Partition.
- Tribal rulers can also be challenged by other tribal characters for their titles via personal combat (duel).
- Tribal rulers pay for men-at-arms using prestige instead of gold.
- Tribal rulers can raid (unless their religion forbids it).
- Once per lifetime, a tribal Ruler can use the Subjugation casus belli.
- Tribal rulers cannot prevent their vassals from declaring war, and cannot imprison vassals or courtiers without passing level 2 tribal authority.
- −50% Title creation cost.
- −20 Opinion with feudal, clan, and republic vassals.
Tribal vassals contribution
Tribal Vassals provide taxes and levies based on the Liege's Level of Fame.
For each level of fame, a character tribal vassals will contribute an additional 8% of their taxes and 15% of their levies, starting at 0% for both when the liege is 
Disgraced, and ending at 40% taxes and 75% levies when the liege is 
The Living Legend.
| Level of fame | Secular opinion
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Tribal Vassal Tax
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Tribal Vassal Levies
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 Disgraced
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−10 | −1 | 0% | 0% |
 Established
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0 | 0 | 8% | 15% |
 Distinguished
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+5/+3 | +1 | 16% | 30% |
 Illustrious
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+10/+5 | +2 | 24% | 45% |
 Exalted among Men
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+20/+10 | +3 | 32% | 60% |
 The Living Legend
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+30/+20 | +4 | 40% | 75% |
Reformation
Reforming tribal government is significantly easier if the tribal ruler swears fealty to a non-tribal liege, as it only requires the ruler to adopt low tribal authority (and have an organized religion). Remaining independent requires the ruler to go all the way to absolute tribal authority and imposes other conditions.
Reforming from a Clan government to a Feudal government and vice-versa is normally not possible. There is however a 'gamey' way in doing so, but it will take some time and planning: By ensuring that your heir inherits a title of the other government form before inheriting your(s). This will however require a similar or a higher tier of title. For example: You have the Feudal kingdom-tier title of Sicily, and want to become a Clan. You make sure that your son and heir inherits the Clan kindom-tier title of Valencia, before inheriting your title of Sicily. He will then become a Clan. Once he inherits your titles, they will switch to the Clan government form as well.
共和制
共和政（Republic）政体は、首都のある所領が都市（City）であるキャラクターが使用します。さらにいうと、そのようなキャラクターはプレイ不可です。共和制の封臣は常に20%の税金と10%の徴募兵を彼らの主君に供出します。
神権制
神権制（Theocracy）政府は、
神権制の聖職者の伝統の教義を持つ宗派にのみ利用可能であり、寺院（temple）を領国の首都とするキャラクターによって使用されます。神権制政府はプレイ可能ではありません。神権制の封臣は、主君の献身レベルに応じて税金と徴募兵を供出します。Realm Priests receive vassal income at a rate of 25% from Realm Priests belonging to their liege's direct vassals. They also provide up to 50% of their income from directly-controlled churches and their vassal priests to their feudal liege, scaled based on opinion.
| アイコン | 献身レベル | 聖職者の評価
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神権制の封臣の税金
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神権制の封臣の徴募兵
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咎人（Sinner） | −10 | 0% | 0% |
   
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忠実な信徒（Dutiful） | 0 | 15% | 10% |
   
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信心深い（Faithful） | +5 | 25% | 20% |
   
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献身的なしもべ（Devoted Servant） | +10 | 35% | 30% |
   
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美徳の規範（Paragon of Virtue） | +20 | 45% | 40% |
   
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宗教的イコン（Religious Icon） | +30 | 55% | 50% |
Lay Priests and Castles
With the Lay Clergy doctrine, churches function identically to castles. Castles are limited to normal obligations, giving 10% of their domain tax to the liege and 25% of their domain levy.
Holy order
- メイン記事へ: Holy order
Holy order government is used by characters who own a holy order title and is not playable. They may own land, but usually (and initially) lease holdings from feudal rulers of their religion, typically cities. Holy order vassals do not pay taxes or levies, but allow their armies to be hired for free.