Genghis Khan Builds an Empire 1211

In 1175, at the age of 13, he became chief of a small tribe of Mongol herdsmen. He used his position to unite a constellation of tribes under his rule, then converted those tribesmen into an army so formidable none could stand against it. The Mongols rode in hordes, sweeping away everything in their path. In 1211 they began their conquest of China. Later, they overran Persia and the Arab civilization of present-day Iraq to the west, and parts of Korea, Burma and Vietnam to the east and south. Nearly all of Russia fell before them too. Everywhere they rode, the Mongols left devastation, sometimes slaughtering entire cities. After Genghis's death in 1227, his successor, Ogadai, stormed through Poland and Hungary, reaching the banks of the Danube River. 

The Mongols subdued more territory than anyone in history. Their influence on human development was overwhelmingly destructive, though as a result of their depredations, East met West. Mongols--in particular, Genghis's grandson Kublai Khan, who completed the conquest of China in 1279--brought foreigners into their realm to serve as administrators over vanquished masses. An Italian named Marco Polo later astounded Europe with news of such Asian innovations as money made of paper and a stone called "coal" that could be used for fuel. 
The size of the empire was ultimately its undoing, and within a few decades it began to fragment. In China the finishing blow came in 1368, delivered by Zhu Yuanzhang, a peasant whose talents for military and political organization rivaled those of Genghis Khan himself.