http://wikibin.org/articles/list-of-atrocities.html
Mongol Empire
Quoting Eric Margolis, Adam Jones observes, in his book Genocide: A Comprehensive Introduction, that in the 13th century the Mongol horsemen of Genghis Khan were genocidal killers (génocidaires)
who were known to kill whole nations leaving nothing but empty ruins and bones. Many ancient sources described Genghis Khan's conquests as wholesale destruction on an unprecedented scale in their certain geographical regions, and therefore probably causing great changes in the demographics of Asia. For example, over much of Central Asia speakers of Iranian languages were replaced by speakers of Turkic languages.
The eastern part of the Islamic world experienced the terrifying holocaust of the Mongol invasions, which turned northern and eastern Iran into a desert. Between 1220 and 1260,
the total population of Persia may had dropped from 2,500,000 to 250,000 as a result of mass extermination and famine.
Before the Mongol invasion, Chinese dynasties reportedly had approximately 120 million inhabitants; after the conquest was completed in 1279, the 1300 census reported roughly 60 million people. About half of the Russian population died during the Mongol invasion of Rus. Historians estimate that up to half of Hungary's two million population at that time were victims of the Mongol invasion of Europe.
The Pope Innocent IV’s envoy to the Mongol Khan, who passed through Kiev in February 1246, wrote:
"They attacked Russia, where they made great havoc, destroying cities and fortresses and slaughtering men; and they laid siege to Kiev, the capital of Russia; after they had besieged the city for a long time, they took it and put the inhabitants to death. When we were journeying through that land we came across countless skulls and bones of dead men lying about on the ground. Kiev had been a very large and thickly populated town, but now it has been reduced almost to nothing, for there are at the present time scarce two hundred houses there and the inhabitants are kept in complete slavery."