I've had it happen a few times where I've dug right into the mountain, created storage, created training area, had my keeper train to level 7 or 8. Made a library and boom, knights attack. No attacking cows or horses or peasants. I've also had a few where I've slaughtered pretty indiscriminately and nothing attacked me. I figured out pretty quick that those peasants could be the trigger, but I've altered my play style and didn't really change anything. I wonder if some other attack (lizardmen or dragon) attacking peasants is triggering it? Or maybe a tree spirit that you've created by chopping too much wood? Just wondering if those attacks could also cause it.

He did say that was a something he was thinking about implementing. I think it would be good to have levels of difficulty, like on easy they gave you that message and were a bit more lenient about it, only attacking if you took out X peasants. While medium difficulty you didn't get the message and they were more likely to attack (maybe about as much as they are currently), and hard they just came at you if you even glance at a peasant the wrong way. 🙂