There was a huge industrial boom post-WWI. At least in the US, there was also a big agricultural boom in addition. See Ken Burns' "The Dust Bowl" for a very sh

There was a huge industrial boom post-WWI. At least in the US, there was also a big agricultural boom in addition. See Ken Burns' "The Dust Bowl" for a very shallow treatment of it. The Mongols were advanced in ways and not in others. The Aztecs ( really, the Mexica ) were as well. The Aztecs come off as bloody. At least for the Mongols, once a conquered place knelt, they were left alone ( outside of taxes ) and were now on a trade network unlike what had ever been seen, which generally raised standards of living. For a blinding array of reasons, things ground to a halt in the Interwar period, leading to the Depression. WWII ended that... Our collective, international inability to manage monetary policy lead to something like 4% of humanity being put to the sword. So who's bloody now?