6. He was responsible for the deaths of as many as 40 million people.
While it’s impossible to know for sure how many people perished during the Mongol conquests, many historians put the number at somewhere around 40 million. Censuses from the Middle Ages show that the population of China plummeted by tens of millions during the Khan’s lifetime, and scholars estimate that he may have killed a full three-fourths of modern-day Iran’s population during his war with the Khwarezmid Empire. All told, the Mongols’ attacks may have reduced the entire world population by as much as 11 percent.
Long way to go to catch up to Chairman Mao. @ 70 million.