So I read
this thread, where setting entities to like each other's sites caused mass genocide. I decided to do something similar. I made a entity of Dragon-ruled crusader dwarves and another of invading Fire Imps. To keep things sane, I set each to only generate one civ. Both of them were also set to want Dark Fortresses.
After fighting through a few technical issues, a world generated successfully. The evil civilizations and the invaders were in the north. All the dwarves were in a small corner in the south.
The first warning sign was that the crusaders didn't show up on the adventure screen. That's odd, I thought, but maybe it won't start adventurers in Dark Fortresses. So instead I picked a nearby dwarven civilization to start in.
Several minutes later, I found a 'dark' fortress. There were goblin coins scattered in it's outskirts. I immediately assumed that they had invaded. However, further inspection revealed no one was there at all! That was the second warning sign.
Then I went from dark fortress to fortress, to find all of them abandoned. They all also had random scattered coins, so I assume that that's just part of their generation. In desperation, I opened up up Dwarf Mode to settle a dark fortress and make art images.
I randomly glanced at a dwarf's profile. They worshiped Togal the dragon-god. Clearly, Togal was still alive. But his empire didn't any cities left! What gives?
Then it dawned on me. The only possible explanation was that THE ENTIRE CIVILIZATION moved ACROSS THE ENTIRE MAP to invade the north! Now that's hardcore. Someday, assuming that migrants keep making babies, Togal and his dwarf horde shall descend upon the dark fortresses of the north and slay them all. If not, Togal shall slay quite a few before dying to a random arrow. Either way, it's still epic. Now all I need to know is where he is, and I can join his dragon dwarven death march.