It was supposed to be a match made in heaven. Capitalism and democracy, we’ve long been told, are the twin ideological pillars capable of bringing unprecedented prosperity and freedom to the world. In recent decades, the duo has shared a common ascent. By almost any measure, global capitalism is triumphant. Most nations around the world are today part of a single, integrated, and turbocharged global market. Democracy has enjoyed a similar renaissance. Three decades ago, a third of the world’s nations held free elections; today, nearly two thirds do.

Conventional wisdom holds that where either capitalism or democracy flourishes, the other must soon follow. Yet today, their fortunes are beginning to diverge. Capitalism, long sold as the yin to democracy’s yang, is thriving, while democracy is struggling to keep up. China, poised to become the world’s third largest capitalist nation this year after the United States and Japan, has embraced market freedom, but not political freedom. Many economically successful nations—from Russia to Mexico—are democracies in name only. They are encumbered by the same problems that have hobbled American democracy in recent years, allowing corporations and elites buoyed by runaway economic success to undermine the government’s capacity to respond to citizens’ concerns.

Of course, democracy means much more than the process of free and fair elections. It is a system for accomplishing what can only be achieved by citizens joining together to further the common good. But though free markets have brought unprecedented prosperity to many, they have been accompanied by widening inequalities of income and wealth, heightened job insecurity, and environmental hazards such as global warming. Democracy is designed to allow citizens to address these very...