I understand that. That's why my suggestion was for it to be a mostly-automated process, with perhaps a human GM having limited influence over things. This would reduce the workload by a huge factor.
Ya, just have it based less on RP and more on just fighting them off.
Let a human GM, determine general invasion strategies (what areas to focus troops, when to retreat from certain areas, how aggressive to be, etc...) but don't both with them actually playing an individual set of characters of daimons or monsters or undead or some such.
Much less work involved for the GM then.
