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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.
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 is can't be annexed, it can't be vassalized, in other words. This cost is be 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 that whose provinces contain cores of nations which don't exist. To release vassals, you must be at peace - wars with Hordes count as war normally. The option is accessible from the domestic menu, in the flag tab.
Vassals you release are modeled on your own nation. They receive your government type, your state religion and it appears that they receive your slider setup as well. More research is needed to ascertain what happens to their technology group and research. Missionaries active in provinces the vassal receives are retained.
Creating a vassal in this way lowers infamy by 2 per province released.