The Southern Russian princes had come close to organized resistance; the Northern princes, terrified, could not unite and were wiped out one by one. After a ten-year quiet which was almost as terrifying as the first onslaught (the Mongols had gone home to attend the coronation of Ogodai as Genghiz's successor), they returned, annihilating the Bulgars, another former enemy of Russia, then turned on the Northern princes.
The next century was smoke, blood, disaster. The only stories the Russians could use to console themselves were of the sort conquered people always tell: grand defiance, magnificent gestures which have no hope of altering the fact of defeat. The Princes of Ryazan, marching out to meet certain death, were offered a deal by the Mongols: "If you want peace, give us a tenth of your wealth." The folk tales have the princes saying in grand disdain, "When we are dead, you may have the whole." The Mongols' reply, not recorded, would have been something on the order of, "OK; thanks!"
When Fyodor of Ryazan had died in due course, his wife, Euphrasia, followed the practice of virtuous wives, choosing to leap from the terem (harem) rather than face the fate worse than death. There's no proof she did so; these stories are the only way the defeated humans could go on living under alien rule.
The Russians gleaned from the great disaster only the bitter consolation prizes of defeated peoples, above all the right to explain what went wrong, whatever went wrong, as legacy of "the Mongol yoke." It's easy for Westerners to mock this sort of grand version of "I had a bad childhood," but it's even harder to imagine Voltaire and Hume springing up on soil that had felt the Mongol ponies' hooves. They were unlike anything before; they were good enough reason to explain many things, above all disappearances and vanishings..
The Mongols specialized in vanishing and making vanish. They didn't build cities, they erased them. Karakorum, the Mongols' one attempt to build a capital city, is a rectangle of mud walls now. The Mongols' greatest memorials are negative: huge blank spots on the map. Eastern Iran, once a populous, irrigated land, is a blank now, courtesy of the Mongol cleaners. They erased the cities and, far more devastatingly, the irrigation systems. Humans breed like cockroaches, and will always repopulate plundered cities--but if you smash their water supply, they can't come back.
The Mongols were the original Aliens: they came, they saw, they erased. They didn't "fight" their opponents, any more than people "fight" cockroaches.
But the one quality which sets them apart from every other tribe is their utter, superhuman immunity to the God-virus. The Mongol attitude to religion was wholly alien. They found the religions of the conquered humans handy, to keep the livestock under control, but could see no difference between the various superstitions and were equally sardonic about all of them. They cared no more about the beliefs of their subjects than a farmer cares what his dairy cattle think about reincarnation. It's true that Genghiz disliked Muslims perhaps more than subjects of other cults, but only because the Khan's armies encountered more opposition from the Muslims, while the Christians, far weaker in Central Asia, were mostly preachers--entertainers on dull nights after a day of erasing villages.
No human tribe has ever managed to keep from catching the God virus-but then, the Mongols were not human. All the survivors agreed on that. An Armenian priest describes them:
"They were terrible to look at and indescribable, with large heads like a Buffalo, narrow eyes like a baby bird, a snub nose like a cat, big snouts like a dog, narrow waists like an ant, and short legs like a hog. They are as strong as lions but as shrill-voiced as hawks....They bear huge litters like snakes and eat like wolves. Death does not appear among them, for they live 300 years. They do not eat bread at all."