[numskully]

Ashen could kill all their own people by pilage, thereby creating a baren wasteland that will never supply invading troops, right? Considering that Ermor troops are summoned, not bought, and don't need supplies, this seems to have no downside. Am I missing something?

no downside for ermor for pillaging your land, unless you buy/cast eating troops (which ermor Users dont really do).

might want to try to keep a province pillage free for sages, to do some research (library magic site). and if your buying sages for research, some of them would end up with a nature path, providing some food for the sages.