But there is another side of the story that we should not forget, so here are five reasons why the Mongols might not be so great. One, here is Genghis Khan's definition of happiness. The greatest happiness is to vanquish your enemies, to chase them before you, to rob them of their wealth, to see those dear to them bathed in tears, to clasp to your bosom their wives and daughters. Off topic, but if that quote rings a bell, it might be because Oliver Stone blatantly plagiarized Genghis Khan in the movie Conan the Barbarian. Two, is an extension of one, the Mongols were seriously brutal conquerors. I mean, not uniquely brutal, but still. The Mongols often destroyed entire cities, and most historians estimate the number they killed to be in the millions.