Rebels are AI controlled enemies that are spawned in counties with revolt risk. Revolt risk measures how upset the population of that county is, and determines if rebels will be spawned there by a percentage meter.
Rebels in Vanilla CKII[]
In Vanilla CKII (Non-Old Gods Expansion CKII) rebels appear in groups of hundreds and thousands of hostile enemies in a single flank under a single leader. The power of the rebels by their technology is unknown, but it is speculated that the technology in the country they were spawned in affects their power. While the leader acts as an actual entity, it is impossible to reason with him or even interact with him short of killing him in the battle. The effects of rebels capturing a county or barony are unclear at the moment.
Rebels in The Old Gods DLC[]
While rebels in vanilla CKII are faceless monsters whose motive is unclear, Rebels in The Old Gods have their own motives to the same goal: Land and independance. Usually, rebels will spawn according to their highest percentage revolt risk, which will usually be religious differences. Rebels are much stronger now, usually splitting into armies of 2 or 3. The leaders of the rebellion will usually be peasant leaders or heirsarchs (Military and Religious fanatics) that will declare war against the holder of the county they spawn in or their liege. If unable to defeat the rebels, and the rebels are successfully able to siege a provence, they might demand any sieged holdings be turned over to them. The leader will become the new liege of those counties, and will become independant. If the rebels are defeated, then the leader will be imprisoned and will get the Broken Spirit trait, which makes him relitively useless, as it subtracts 10 from marshal, 4 from every other skill, 30.00% from fertility, and 2 from health. the victor of the rebellion war (As it is now treated as a war) will get an amount of prestiege, and if the rebellion was for religious differences, then Piety will be gained by the victor.