I'm wondering if there's some peasant mechanics that can be introduced to encourage war. Similar to how peasants get mad when you're at war for too long, they could get mad when you aren't at war often enough.
We tried this. It nearly killed the game, because it introduced a vicious cycle: there's not enough war, so peasants get upset (manifesting as trouble with regions), so trying to go to war would be far too dangerous, so we have to fix up our regions, so there's not enough war....etc.
Or maybe have peasant armies attacking other regions to strike out on their own. They could have the banner of the realm they spawn from and everything, but make players have absolutely no control over them.
That wouldn't achieve anything except to annoy people. If Realm A doesn't want to go to war with Realm B, peasants from Realm B attacking Realm A (which everyone knows is not being done by the players) will do nothing to provoke a war. If Realm A
does want to go to war, sure, they could use the peasant attack as a pretext for war, but they could also use any of a dozen other things that already exist.