It’s hard to remember now, but in the days immediately following the attacks of 9/11, a spirit of religious unity reigned. Shocked political foes gathered together at the Washington National Cathedral for a prayer service that included a Muslim imam who read verses from the Koran. Just a few days later, George W. Bush quoted from the Koran himself at the Islamic Center in Washington, and told the country that “Islam is peace.”

It didn’t take long, however, for the tender feelings of togetherness and tolerance to be replaced by division and hostility. Some thought leaders and policymakers embraced Samuel Huntington’s idea that the West was engaged in a “clash of civilizations” with Islam. Meanwhile, neo-atheists led by Sam Harris and Christopher Hitchens put forward their own theory of a world split between civilized secularists and dangerous religionists. Secular academics and other thinkers have predicted and hoped for decades that as societies become more advanced, religion and its institutions would become less relevant. To them, 9/11 was further proof that religion is incompatible with modernity.