W ill globalization destroy itself? Every few years, another crisis suggests it might. The Internet, satellite phones, and intercontinental air travel help terrorists cross the world in an instant. The global spread of democracy shakes authoritarian governments–and opens the way for Islamists in Tehran and Cairo, a populist strongman in Venezuela, and nuke-happy nationalists in New Delhi. Open capital markets wreck the economies of Southeast Asia. Divisions between Muslim immigrants and the rest of Europe explode in French riots and Dutch assassinations.

These unhappy stories are familiar by now. An open, mobile, interconnected world creates new threats, or amplifies familiar ones, and countries throw up new borders in self-defense. The uncertainties of political and personal freedom make invented traditions seductive: pure Islamic states, India for the Hindus, premodern idylls available for free download.

But, along with electronic commerce, transnational fanaticism, and increasingly fluid borders, there is a missing piece in the current picture of globalization, one that puts the familiar paradoxes in a new light: biopolitics, the politics of human life and reproduction. Around the world, people are taking control of childbearing in new ways, which could produce serious consequences for global politics. In Europe, Russia, Japan, and South Korea, women are having too few children to sustain the current population. A shrinking workforce means too few taxpayers to support the next generation of retirees. The only obvious solution is greatly expanded immigration–which, recall, is already the source of riots, xenophobia, and deep political anxiety. All this threatens a perfect political storm of bankrupt welfare states, struggles over immigration, and crises of national identity. Meanwhile, in India, China, Taiwan, Pakistan, and Afghanistan, a very different problem is growing. Abortion of female fetuses, along with other causes, has produced a population with roughly 100 million more men than women–men who are a prime constituency ...