1. Being a very successful social climbing mass murderer and tyrant still makes you a mass murderer and tyrant.That assessment is pretty unfair.
1. He pretty much absorbed those empires, taking their knowledge and technology for his own purposes. This guy started out living in a yurt, and by the end he employed more mathematicians and engineers than anyone else on the planet.
2. While he was brutal in his methods, this has been misrepresented. Genghis Khan was the absolute world champion of all time when it comes to "the carrot and the stick". Voluntarily joining him was almost always a distinct improvement. Opposing him meant you became an example of what not to do. This is a strategy that was likewise employed by Alexander, for instance.
3. Speaking of improvements: great inventment into infrastructure, practically-minded policy of religious freedom, considerable reduction in tax burden, categorical tax exemption for the poor, removal of corrupt governors... For most people, being conquered by the Mongols was more like being liberated. (And sure, that's for the ones who didn't happen to live in a city that resisted... but on average? Genghis Khan improved far more lives than he ended.)
4. After he died, his empire still lasted over six decades. That's impressive, when you consider that the general rule is "fast rise, swift fall". See also: Alexander.
5. The Mongol successor states were new iterations of the empires he had conquered, so saying he broke them isn't really accurate. Or did Persia and China no longer exist, after his time?
2. Thing is, when he used the stick millions of people were the victims, no mercy or pity seen, in a way which was uncommon for Medevial armies.
3. Yes these are all good things, but there are other instances. I also happen to know the mongols also very often used for horrid expropriation.A system where if you didn’t pay up, not only you, but your entire family and province would be anihlated, where fields would be left with dead bodies for decades after and create social problems which last centuries later (See Russia)
4. Fair cop. In which time they did even more damage, see finishing up the conquest of Russia, burning Baghdad and waging more unending war on China.
5.Funny you bring up Persia and China. Persias population was hit so hard by the Mongols they were pushed down to Bronze Age agriculture and didn’t recover there numbers until 1950. China had to be brought in whole in a brutal conquest and even then, the Yuan dynasty was never regarded as a legitimate dynasty and thrown out in a Peseant rebellion.And of course, Russia, where the Mongols destroyed the center of Russian power in Kiev and created the fundamentally gangster dynamics we see continue onto this day by making Nobles there tax collectors, with the implicit threat of burning down them and all that they loved and cared about if they didn’t extract as much as possible, creating poisonous social incentives, only perpetuated to this day.