I mean, who could ever forget how Genghis Kahn invaded Vietnam?
Didn’t see your post before I posted. Great minds think alike!
How many great armies stood in his way.
Because for the most part he didn't fight the battles in person? Because other generals (including some of his sons and whatnot) were the actual victorious (or not) generals? Because it took 23 years for him to defeat his most powerful enemy, the Jin Dynasty? Because his mob of mass-murdering cutthroats were mostly similar to many a people attacking on horseback, going back to antiquity? OTOH, he may have been the greatest mob boss in history...
Genghis Khan and his successors in that dynasty remind me also of the Assyrian Empire -- the Assyrian army would arrive, set up a siege and/or beat their victims in battle; the longer it took and more expensive it was, the higher the amount of tribute they'd levy on their conquests. If that amount was unrealistic and basically unbearable, the newly conquered were more likely to not send the tribute, which would result in the arrival of an Assyrian army which would again kick their asses. One difference is, the Assyrians had periods of ascendancy off and on for over a thousand years, and the Mongolian empire was around for perhaps 150 years, and only in a divided state (IOW, it wasn't a single monolithic empire).