I don't really know either then. Might be very random or bugged. My playthrough is pacificst so I don't really get wars since progeny don't seem to start them after the whole eloping ordeal. All I know is you can just ask for peace from the attacking reign if you have enough affinity if you want it to stop.Well, I don't know. Other sieges where I defended, I had to fight 10 or so battles before it was lifted and the attacking reign was repelled. Still, there seems to be no end to the number of siege battles of this port.