Guide to Vassals
Vassal states are factions that have come under the stewardship of another faction. The vassal pays 20% of its income to, and gains military protection from, the vassal master; any third party that declares war on one automatically declares war on both. Likewise, going to war with a vassal master triggers an automatic declaration of war against their vassals.
Vassals are not slaves to their vassal masters. They can still conduct themselves as semi-independent factions – conducting diplomacy and private wars, expanding their territory and so forth. They must however seek permission from their vassal master before declaring war on another faction.
There is an entire category of diplomatic options purely for vassals and vassal masters. One faction can attempt to vassalise another, or choose to become another’s vassal. A vassal may request liberation, or a guarantee of liberation further down the line. They may also declare their independence, which puts them immediately at war with their former master.
A vassal master can liberate their vassal, restoring them to fully-autonomous faction status, or promise to liberate them later on. They may also choose to annex their vassal, taking full ownership of all their settlements, characters and armies and effectively liquidating them as a faction. However, promising to liberate a vassal then later annexing it is a grave act of treachery, and will negatively impact the vassal master’s trustworthiness rating. In addition, a master with multiple vassals who annexes one will suffer a major diplomatic attitude penalty with all his other vassals.
Otherwise, the usual rules of diplomacy apply. Vassals and masters have their own diplomatic attitudes towards one another, and may manage relations, trade food, make trade agreements, lend and borrow money, and in short, conduct diplomacy as normal between themselves and with others.