It took many centuries for Christendom to achieve this thick form of pluralism. Whether the Islamic world can move toward its own, culturally distinctive version of this democratic virtue is now one of the largest geopolitical questions of the 21st century.

Some argue that Muslim theology — emphasizing fidelity to its conception of divine law — makes this unlikely (or impossible). Others point to past centuries when Muslim majorities and rulers coexisted with large Arab-Christian populations — a thin form of pluralism in which Christians were second-class citizens but not subject to violent intolerance. Every major religious faith contains elements of tribal exclusivity and teachings of respect for the other. The emergence of social pluralism depends on emphasizing the latter above the former.

Promoting democratic institutions is no easy task in the midst of revolution and civil war. But even limited levers — stronger condemnation of abuses, conditioning aid on the protection of minorities, supporting moderate forces in the region — are worth employing when the stakes are so high. America, however, seems strangely disengaged. “One of America’s oddest failures in recent years,” argue Economist editors John Micklethwait and Adrian Wooldridge, “is its inability to draw any global lessons from its unique success in dealing with religion at home. It is a mystery why a country so rooted in pluralism has made so little of religious freedom.”