So we all have seen that our favorite evil entities are no longer very evil. The problem is that there really isn't that many things to encourage hatred between the sentients. So here's a few ideas, some that only need to be ephemerally used during worldgen, some that have a "physical" influence on the DF world:
1. Missionaries - Since DF now has religion there seems to be a gap in how religion spreads. So why not have temples send out "missionaries" to other cities/towers/forests/caves/mountains/etc? Basically it'll work like the "Scouted the region" or "Wandered the wilderness" legends entries and involve the temple sending a missionary out to a target. If some people are successfully converted the town local areas (temple's location and target location) become closer friends. If the missionary is killed or turned back the hatred grows. If the missionary was from the leader's temple, war breaks out.
2. Sacrifices - Still on the religion thing, why not have "evil" spheres perform ritual killings? That'd piss people off. Just flag the entity as dead and flag the civ the religion belongs to.
3. Minor temples - There's always the big temples, they're all well and good. But what about smaller onces. The size of hovels and containing only a small altar and a priest. What does this have to do with war? If the goblins (at peace with the dwarves) built a small temple to their demon god in the human city that contains the more entrenched temple to the human's god of crops or whatever, wouldn't that light some fires?
4. Levels of devotion meaning something - So Urist is a devout follower of the god of forges, so what? What does that mean? Well, the lack of Caravan Arc removes the reason for 80% of wars in human history, so what about that last 20%? Religion! If Urist and all his friend are devout, would they tolerate that temple to the demons even existing? So Urist goes and attacks the goblin priestess. The less devout stand back while the completely enshrined join arms to kick some ass. Thus leading to what politicians call "an international incident". The goblin's demon gets pissed that his temple was sacked and goes out to do a little sacking of his own. Yay!