Actually, the Mongols were perfectly happy to let everyone live, provided they got their tribute. What’s more, the Mongol empire was the first country in the world with universal religious toleration and constituted a free-trade zone almost the entire length of Eurasia. Because the Mongols, unlike the Teutonic Knights, were perfectly happy to let the Rus remain Orthodox Christians, St. Alexander Nevsky made the Republic of Novgorod tributary to the Mongols so he could turn his military attentions against the northern Crusaders.
In a way a shame the Mongols’ attitude toward hygiene was as retrograde as their attitude toward religion and commerce was forward-looking: they collapsed due to infectious diseases the spread of which was facilitated by the Mongol abhorence of bathing.
And they made some wicked BBQ too!