Can't trigger victory condition in Genghis Khan campaign level 6

I have killed every single enemy unit and building except walls and I still can't trigger a victory condition. I even researched Spies (for 200 gold, apparently that means he has 1 villager left? but I couldn't find the villager) and it revealed the remaining bits of map but no new buildings or units.

I thought to win a conquest victory all you had to do was destroy every town center and castle. I can't seem to trigger a win in this level.