I don't believe the Mongolian Empire portrayed themselves as less righteous than the civilizations they conquered. They acquired a bad reputation ex post facto and in lands out side there influence. Much like some of the polices the U.N. via and or U.S. powers carry out today are taught to be believed as the struggle of the righteous. How will we read?
The problem with the Mongolian Empire is they happen to conquer people who could also read and write and they didn't establish Mongolian as a francalingua, instead opting simply to learn the language of the conquer or using Arab or Chinese which many people already knew. Survivals would also go to other countries and tell them how horrible it was is that those countries could also put it down as Mongolians were crazy, even if their rule comparatively to the time wasn't too unusual. So it's a case of the conquerers not writing history.
Not the history we read to today. It would be very disappointing if eventually, in the event of another global land grab, let us just for kicks say the U.S.A. was said conquest; (Better yet lets say You vs. Me); that the usurper did not make some "Right" over Wrong argument on there behalf. In which to the victor go the spoils of war, not limited to, but to a Large extent including the accepted dictation of history. Of which some of it must contain a justification and implication of Right doing in your actions as well as a lot of sweeping under the rug. This will be globally distributed on a scale (well you know). Okay now your the victor, anyone who did not like me more than you was was just downright disgusted with my ages of Authoritarian rule, would then jump on the bandwagon smear campaign. But pockets of upheaval and unrest here and there as well as poor Frank over there whom you trampled to get to me would be reeling; writing another history. And when you got weak, overextended, short sighted, slothful, old and arrogant, low of resources with to much to look after and too few to trust. Here come Frank and sons to the rescue. Unfortunately by then the the dwindling tree population has put tree's on the endangered species list indefinitely. The debaucherous aristocratic elite have seized hold of the worlds supply of paper documentation to support there recycled paper mache diaper fetish and the only source of information is party controlled wold wide web 3.14159 where the last reference of an A. Lincoln was a man attempting to save a country in it's infancy from the separatist cries of the southern and largely Vampire controlled states all while attempting to kick a massive addiction to Intellivision's Pong. Mean while the worlds oceans have receded to the point that, due to fishing bans put in place to save the dolphins, who it turns out just make weird noises and tuna who were really the ancient beings capable of extraterrestrial communication are extinct, are to polluted with the squealing dolphin's feces to drink. Scientists are scrambling to find the lost formula for Orange Tang which they've found is the only thing that makes piss palpable (no water). And no one wants to be here because quit frankly were the itchy hemorrhoid on the galaxy's ass. Doesn't history require a little imagination, very little evidence and a whole lotta hearsay, oh I almost left out "I'm Rightness".