When I posted this question, I sort of felt I got shouted at for mechanics/stupidity, but perhaps that's just my paranoia
I play SP only (I would suck at MP, and have no commitment time), latest game up to one notch below Impossible AI (will try that next time). I was reflecting that in my games, I don't think I've reached "End Game", I've won before then. In my games, I build a couple of forts in the "Early" Game. But in the "Mid" Game I just capture AI forts, and never bother having to build a fort again. I guess I was wondering about self-imposing a rule that I had to destroy any forts I captured, to make it more interesting to have to build forts again, or see how the dynamics would change if having to rebuild forts at fronts or rely on longer home rebuilds.
I'm sure there are other strategy games where when you "capture" and enemy land something like the fort gets destroyed, not handed over.(?)