ISIS' army has attracted a stream of Western volunteers, but there is no reason to panic about their return home. Some may come back as terrorists, but the danger has been exaggerated, and the United States and the EU know how to handle such problems.

With U.S. hegemony waning and no successor waiting to pick up the baton, the current international system will likely give way to a larger number of power centers acting with increasing autonomy. The post–Cold War order is unraveling, and it will be missed.