Minor Annoyance
Deity
If they only have 2 cities they will almost certainly cause the capitulation bug if you do vassalize them. The bug will basically block any other civs capitulating to you due to a really small oversight in the capitulate code.
AIs take into account the power level of other civs not involved in the war, for some reason this includes insignificant civs that will have absolutely no impact on any war. The biggest problem lies in it even considering the vassals of a person its at war with.
Its usually a result of having extremely weak civs on the map and usually thats the result of capitulating civs you've smahed into the abyss. It's incredibly annoying and really, really stupid....
TMIT knows more than me on this though
But DEFINATELY wipe them out.
Is this accurate? Has any changes made in better AI altered this behaviour?