Fareed Zakaria in The New York Times:
The world has been horrified but also puzzled by the rise of ISIS. How does one comprehend its brutality and success? What is its likely path? In March 2015, The Atlantic offered an answer, in an analysis by Graeme Wood that quickly became the most widely read essay in the magazine’s 158-year history. Titled “What ISIS Really Wants,” it focused on the ideology that animates the group. Understand its ideas, Wood suggested, and you will understand the phenomenon and how to fight it. Many other, more polemical explanations of jihadi terrorism today — from Bill Maher to Sam Harris — also shine a spotlight on the ideas behind the mayhem.
Most intellectuals think ideas matter. In one of his most famous and oft-quoted lines, John Maynard Keynes declared, “Practical men who believe themselves to be quite exempt from any intellectual influence are usually the slaves of some defunct economist. Madmen in authority, who hear voices in the air, are distilling their frenzy from some academic scribbler of a few years back.” Scott L. Montgomery and Daniel Chirot concur, arguing that ideas “do not merely matter; they matter immensely, as they have been the source for decisions and actions that have structured the modern world.” In “The Shape of the New: Four Big Ideas and How They Made the Modern World,” Montgomery and Chirot make the case for the importance of four powerful ideas, rooted in the European Enlightenment, that have created the world as we know it. “Invading armies can be resisted,” they quote Victor Hugo. “Invading ideas cannot be.”