It was once the great dream of Western liberal culture: a stewpot of different religions, races, and ethnicities, harmoniously blended. But German Chancellor Angela Merkel has pronounced the dream dead. Multiculturalism, she said, has failed, utterly failed." Merkel is a respected world leader, not a nationalistic xenophobe, so her emphatic finality is all the more startling. But many Germans and many Europeans share her pessimism. The continent is recoiling from an influx of immigrants, especially those from Muslim lands: The French and the Belgians have banned burqas; the Swiss, the construction of minarets. Anti-Islamic movements are gaining momentum in Italy, Britain, the Netherlands, and even Sweden.

To dismiss these tensions as mere intolerance is, I think, naïve. The boundaries between cultures are eroding, due to widespread immigration, economic interdependence, and the Internet, forcing modern societies into an uncomfortable paradox. We believe that every cultural group, religion, and nation has the right to self-determination. But we also hold as a bedrock principle that every human being is born with inalienable rights — including the 50 percent of us who are women. Is it our business to free Muslim women from their shrouds and subservience, to bring a halt to female genital mutilation in Africa and the Middle East? Do we have the right to object to China’s insistence that democracy and human rights do not apply there? Genteel tolerance alone will not resolve these questions. The collision of values has begun. How that conflict plays out will determine the shape of the next half-century.