What to do about Ermor ....

[magnate]

Of course, it all depends on Ermor's theme. Considering his growing army, you are probably playing against one of the two undead-only themes.

First of all: If he shreds your priests, there haven't been enough priests. Don't rely on bringing your expensive giant priests with you, but rather, hire a swarm cheap indy ones. Don't place them all in one spot. Banishment, which is the key to beat off Ermor (unless you have death magic on your own), has a very long range.

Second, Ermor usually tends to have a very strong dominion. Preaching it out of existence takes its time, and I find it especially obnoxious if the lands that feed your sieging/preaching army are barren.

Ermor gains troops for free, depending on the Dominion of the province (at least, the two undead themes do so, I am actually not sure about Broken Empire), or by reanimating them with priests. In the first case, the quality of the troops is determined by such facts like if there is a castle or temple in the province, and the reanimation process generally requires either corpses in the province or population.

Does this mean that if I reduce his dominion he'll get fewer troops? He's definitely all-undead - I've seen only one or two live units all game, and he brings 100-150 undead into each battle (and animates more during them).

I don't mind how long it takes to preach him out - I've got seven other nations to conquer. I just want the best way to contain him without tying up too many resources. Laboriously taking each of his provinces is going to take a lot of time and a lot of priests and troops. I think the AI tends to focus on a besieged castle, meaning I could mop up the other provinces with less trouble ... providing the sieging force was strong enough ....