Throughout the fourteenth century AD/eighth century H, waves of plague swept out of Central Asia and decimated populations from China to Iceland. So devastating was the Black Death across the Old World that some historians have compared its effects to those of a nuclear holocaust. As countries began to recover from the plague during the following century, sharp contrasts arose between the East, where societies slumped into long-term economic and social decline, and the West, where technological and social innovation set the stage for Europe's dominance into the twentieth century. Why were...