George Friedman thinks...

...U.S. strategy in the Middle East should be about maintaining the balance of power. And I agree: we have no real allies in the region save Israel, so let the rest of the powers "work" it out.

Friedman writes (my emphasis):

Is ISIS really a problem for the United States? The American interest is not stability but the existence of a dynamic balance of power in which all players are effectively paralyzed so that no one who would threaten the United States emerges. The Islamic State had real successes at first, but the balance of power with the Kurds and Shia has limited its expansion, and tensions within the Sunni community diverted its attention. Certainly there is the danger of intercontinental terrorism, and U.S. intelligence should be active in identifying and destroying these threats. But the re-occupation of Iraq, or Iraq plus Syria, makes no sense. The United States does not have the force needed to occupy Iraq and Syria at the same time. The demographic imbalance between available forces and the local population makes that impossible.