Nothing like this has happened in human history. A combination of cultural preferences, government decree and modern medical technology in the world’s two largest countries has created a gender imbalance on a continental scale. Men outnumber women by 70 million in China and India. The consequences of having too many men, now coming of age, are far-reaching: Beyond an epidemic of loneliness, the imbalance distorts labor markets, drives up savings rates in China and drives down consumption, artificially inflates certain property values, and parallels increases in violent crime, trafficking or prostitution in a growing number of locations. Those consequences are not confined to China and India, but reach deep into their Asian neighbors and distort the economies of Europe and the Americas, as well.