In a sense, their evolving strategy acknowledges the timeless nature of war in the Middle East: Owning the desert means nothing, owning oases is everything. ISIS grasped that if they take the cities, everything in between falls into their laps.

Their new approach echoes brighter chapters of our own military past. What the Islamic State’s doing in the desert by ignoring minor garrisons and jumping past to the cities is a sandy replay of General MacArthur’s “island-hopping” campaign in the Southwest Pacific, a strategy of genius based on MacArthur’s insight that he could leapfrog over stubborn Japanese garrisons, fighting only for vital islands that controlled sea lanes or offered airfields. He let the Japanese wither behind his advance.

ISIS is “oasis-hopping.”

Of course, the long-term goal is a global caliphate. That won’t happen. But the caliphate ISIS already has built in the Arab heartlands is going to grow, unless a serious counterforce appears (which means us). On top of that, we’ve misread their mid-term objectives.