Ideas can only be vanquished on the battlefield when they are instantiated in a place with concrete institutions that can be decisively conquered and crushed. The idea that motivates jihadists from Raqqa and Tripoli to Brussels and beyond isn’t like that. It lives mostly in the minds of those devoted to it, and so it can only be defeated by an alternative idea.
The Judeo-Christian and secular post-Christian West is singularly ill-suited to supply such an alternative idea to people consumed by visions of Islamic purity, grandeur, supremacy, and revenge. It will have to come from deep within Islamic civilization itself.
Does this mean that ISIS poses an “existential threat,” as Republicans are so fond of putting it? Not at all. But that doesn’t mean it won’t inspire fear, drain blood and treasure, destabilize economies, undermine civil liberties, and provoke harmful right-wing reactions throughout the West for the foreseeable future.