So here's the thing:
The year is 1125, and most clans are eliminated because they have no new heirs
After defeating the khuzaits (by executing the last noble), I became the new owner of their settlements but some of them didn't surrender to my kingdom
It turned out that the clan that owns the settlement was eliminated a long time ago and apparently I can't besiege that town because the khuzaits no longer exist
It also has to do with the kingdom's decisions (for example, I can vote for a new settlement owner who is already dead)
The year is 1125, and most clans are eliminated because they have no new heirs
After defeating the khuzaits (by executing the last noble), I became the new owner of their settlements but some of them didn't surrender to my kingdom
It turned out that the clan that owns the settlement was eliminated a long time ago and apparently I can't besiege that town because the khuzaits no longer exist
It also has to do with the kingdom's decisions (for example, I can vote for a new settlement owner who is already dead)