Answer to your problem
[ITEM_THIEF] means that they attack based upon thievery and will not actually enter a war, remove this and they should go to war
other problems
[PEARL] currently does nothing as pearls don't exist yet and is only for edible vermin anyways
[FISHITEM] and [GNAWER] are for vermin creatures only
Didn't work, I also took away skulking, becuase that would be a dumbass idea for a warring race.
Play with ethics. Make them lie and steal and murder and let them torture and eat dead enemies... you'll see them go to war, or at least get warred upon.
Trying now.
EDIT: Had about two or three wars, they won every battle. I though that was weird, so I go in as an adventurer, I had metal weapons. Seems they couldn't get wood so they somehow created metals...
I set them to have gem and stone prefrences now, they also can mine.
EDIT2: Holy shit, very effective(I added Tree Cap Diplomacy)! They come in massive numbers now!(More than elves), yet they still use fucking metal weapons, not the stone and gem ones I asked for. They must be able to become alchemists, since they somehow turn stone and gems to metal, without any forge to do so. Awesome.
Now my last question, weaken them, or keep them as they are?