They assaulted my settlement, but then just stood there. Provoking them didn't work either. They just followed me until I entered the settlement, then stopped. It was pretty disappointing. Does anyone else have this problem? EDIT: I have realized it is the immobile artillery that is causing the problem. The AI does not use it, for whatever reason, and if it doesnt have siege engines, it wont move. I think it is a bug that the AI wont shoot the artillery.