Five thousand years ago, use of the wheel began to spread from Mesopotamia across Eurasia, revolutionizing transport and enabling chariot warfare. A millennium ago, the stirrup enabled Genghis Khan’s Mongol hordes to conquer most of Eurasia (coming from the other direction) at unfathomable speed. Paul Kennedy’s seminal Rise and Fall of the Great Powers captures the way technological and economic advances have converted into strategic advantage, and how failure to “lock in” that edge accelerates imperial decline. Over the past three centuries, the spread of industrial technologies gradually weakened Britain while stimulating the United States. The West defeated the Soviet Union not through warfare but by maintaining a superior economic system with higher technological standards. China’s late-20th-century rise is very much the unfinished business of the Industrial Revolution.