In just a lifetime, Genghis Khan created the largest empire that ever was -- larger than what the Romans had done in centuries. The wars led in his name killed some 40 million people (about 10% of the world's population at the time)! But, as a study of the Carnegie Institution's Department of Global Energy showed, these bloody conquests helped the environment, removing nearly 700 million tons of carbon from the atmosphere. He conquered all of modern Mongolia and vast swaths of Siberia within five years. Some of the often-quoted figures are downright outrageous. Estimates of how many people Genghis Han killed range dramatically, sometimes going up to 100 million. However, this isn't necessarily the number of people that Genghis Han killed directly, but also people he killed through famine and hunger.

Source: ZME Science