That leaves patience, containment, and humanitarian aid as the least-bad policies while waiting for this awful war to play itself out. In 2003, David Petraeus, then a division commander in Iraq, famously asked “tell me how this ends?” in reference to the conflict just starting there. It was a good question then, and it’s a good question now. The war against the Islamic State gets a lot of attention, much of it focused on the immediate: Is the war going better or worse this month than last month? Is the Islamic State gaining ground or losing it? Are U.S. air strikes killing more Islamic State leaders or fewer? But these things only matter if they contribute to an ultimate end to the conflict on terms the United States can live with. Will they? In fact, we have a lot of evidence on wars like this and how they typically end. But it’s not a very encouraging story. The Islamic State threat is likely to persist, in one form or another, for a long time. In the meantime, we’re going to be stuck with a policy that amounts to containment and damage limitation, whose shortcomings will frustrate many Americans.