A vassal country is a country, a client state, that is subject to the rule of a foreign country. A country can become a vassal either through diplomatic or military means, and may eventually be annexed peacefully ("diplo-annexed") to the ruling kingdom. There are two ways for a free country to become a vassal of another country: diplomatic vassalization and forced vassalization.
A nation can become a vassal of another in three ways:
- Forced through peace negotiations: no limitations, but generally will only be accepted by a nation with fewer than 5 provinces.
- Accepting a Diplomatic vassalization proposal.
- Choosing to release some of its provinces as a vassal state.
Note: These are considered from the overlord's point of view rather than the vassal's
- 50% of the vassal's monthly tax revenues go to its overlord.
- Overlord receives military access.
- Both nations share fog of war.
- The vassal cannot enter any other alliances.
- The vassal cannot enter any other royal marriages.
- In all versions up to 5.1, vassals would not grant Military access to countries which were at war with the vassal's masters. Since this mechanic was seen as exploitative, the 5.1 patch changes the mechanic by allowing automatic military access through lands of vassals of your enemy.
- Can be called into war by their overlords, whether the overlord is the alliance leader or not.
- 50% of a Vassal provinces count towards the overlord's support limit.
- A vassal can enter royal marriage with their overlord.
- Other nations can declare war on the overlord's vassal.
- The vassal may be disloyal and declare war on the overlord, such as when the overlord is currently being mobbed by many other opponents.
- In Europe there is a need to monitor a vassal's religion if it changes during the reformation then alliances are broken and relations are damaged.
Becoming a vassal
There are two ways for a free country to become a vassal of another country:
If two countries maintain good relations and one is significantly more powerful than the other, the weaker of the two may accept to become a vassal through diplomatic means. Before a country can offer another vassalage, there are some requirements that need to be met:
- They must have a royal marriage
- They must be allies
- They must have very good relations (+190 or better)
- They must belong to the same religious group
- They must both be at peace
- The minor nation must have no more than 4 provinces
Also known as "Force-vassalisation", this option is available exclusively through the Peace negotiation screen. If a country is soundly defeated in a war, the victor may demand that the defeated becomes a vassal. This requires a large war score, which appears to be the sum total of the war value of all their provinces - if their entire nation can't be annexed, it can't be vassalized, in other words. This cost is modified by some rare Casus belli such as Subjugation.
A vassalage can end in three ways:
- The overlord can release the vassal from their liege
- The overlord can be forced to release the vassal as a part of peace negotiations
- The vassal can declare independence
Release vassals is an action that can be undertaken by a nation whose provinces contain cores of nations which don’t exist. One must be at peace to release vassals - wars with Hordes count as war normally. The option is accessible from the overview tab of the domestic management interface.
Vassals assume the government type and state religion of the releasing country, but use their own given technology group, national ideas (according government technology level) and values of the domestic policy sliders. More research is needed to ascertain what happens to their research/technology level. Missionaries active in provinces the vassal receives are retained.
Creating a vassal in this way lowers infamy by 2 per province released.