Settled civilizations only improve inside a fixed way of doing things; Genghis Khan had no fixed way of thinking, and that is why he could absorb any technology he met.

I think that sedentary armies, sedentary civilizations, they get stuck in ways, this is how we do it. And we're going to make it a little faster, we're going to make it a little bigger, a little stronger but this is how we think. Genghis Khan had no set way to think and, when he encountered the first walled cities around 1209 after founding his nation in 1206, he went out on these raids and I really think there were raids not wars at first.