The Mongols destroyed irrigation systems as deliberate policy to return farmland to pasture, not out of the stupidity historians attribute to them.

So they think, a lot of the historians, they think the Mongols are so stupid, they let the irrigation system be destroyed. No, it takes more work to destroy an irrigation system than it does to create it. They destroyed those systems out of a policy, and that was, “This is going to return to pasture land.”