Portrait of Genghis Khan (1162-1227), the Mongol ruler who established the largest land empire in history. After uniting the nomadic tribes of the Mongolian plateau, he conquered parts of central Asia and China. His successors further expanded the empire, reaching as far as Poland, Vietnam, Syria and Korea. At its peak, the Mongol empire covered between 28.5 and 31 million square kilometres, an area the size of Africa. While many were killed during the invasions, Khan granted religious freedom, encouraged trade, and created the first international postal system. He died in 1227 during a military campaign against the Chinese kingdom of Xi Xia.