Can the Islamic State survive?

First, because great powers get war-weary and distracted. As different as our situation is from the aftermath of World War I, it’s clear that the United States would be more involved militarily against ISIS if we didn’t have the recent disillusioning experience of a bloody occupation in Iraq. And it’s easy to imagine events intruding — another economic crisis, a hotter war in Ukraine, brinkmanship with China — that could make Ramadi look as remote to our interests as Arkhangelsk and Vladivostok seemed to the average Westerner in 1919.

Second, because a regime fighting for its survival has an edge over a coalition of less-invested adversaries. Yes, the Islamic State has made enemies of just about every neighboring government and military. But that means its leaders and foot soldiers know that they’re in a victory-or-death situation, which creates incentives similar to the ones that helped the Soviets, and before them revolutionary France, fend off attacks from all comers.

Third, because realpolitik can help even fanatics find allies of convenience. The Bolsheviks came to power in part because Germany deliberately shipped Lenin to St. Petersburg, and Berlin cultivated secret military ties with the Soviets across the 1920s. In a somewhat similar way, the Islamic State has already been funded by Sunni donors from Saudi Arabia, Kuwait and Qatar, and so long as ISIS remains at war with Iran and its proxies, the Sunni powers won’t root unreservedly against it.

If the Islamic State remains permanently at war with them, of course, cooperation will be impossible.