Why does a minor faction attack me once I assimilate it?

I pacified my first minor faction, Bos, by completing their quest. A few turns later I assimilated them. They immediately responded by besieging my city in their native region. What's going on and how am I supposed to respond?

1 Answer

Pacifying a minor faction does not affect roaming armies of that faction currently on the map; it only stops new armies from being spawned in that region. You still have to kill off any roaming armies that were spawned before you pacified the faction.

I think it was only coincidence that one of the armies started besieging your city after you assimilated the minor faction.

2