Virtually every trouble spot on the planet has some sort of religious component. One need only consider Iraq and Afghanistan, Iran, Israel and Palestine, Turkey, India, Pakistan, Russia, and China, to name but a few. Looming behind national issues, of course, is the problem of regional Islamist extremism and transnational Islamist terrorism. In all of these sectors, religious tensions, ideas and actors are of great geo-political importance to the United States. Yet, argues Thomas Farr, our foreign policy is gravely handicapped by an inability to understand the role of religion either...