The Mongol Conquests

Under Genghis Khan, the nomadic Mongols exploded out of the steppe to build the largest contiguous land empire in history, from Korea to Hungary. Their mounted archers, discipline, and calculated use of terror let a few million herders conquer much of the civilized world — and once conquered, that world was stitched together under one 'Mongol Peace' that reopened the Silk Road and let goods, ideas, and eventually the Black Death flow freely across Eurasia. Conquest had accidentally globalized a continent: for a few decades a traveler could cross from Hungary to Korea under a single authority.