Have you considered using religion as a tool of war? I recently did a check of how well Church of Sartan is spread, and 75% of all FEI regions have a 90-100% follower base. Priests could wipe regions away without much effort. But it would turn this entire shindig into a religious conflict, of course.
I mean, not to point things out, but Topenah (95% followers last I checked) has been sitting entirely undefended at Sorraine's border since... well, ever. That was until I informed Velax, of course, that this was a significant leak in our defences. But to reiterate, that is a (albeit small and not fully populated) city with no militia or units present, ready to be taken by a Sartanian priest in the blink of an eye.
I'm not saying that this course would have been appropriate for Sorraine, let alone that the Church of Sartan is worth a damn, but Arcaea is not the big powerhouse you would make it out to be.
