America’s goal should be to help lower sectarian temperatures so that eventually a moderating dynamic replaces the current brutalizing one. The grand strategy should be to help the two sides separate as much as possible while containing the radicals on each side. The tactic should be devolution. Give as much local control to different groups in different nations. Let them run their own affairs as much as possible. Encourage them to create space between the sectarian populations so that hatreds can cool.

This was the core logic of the Biden/Gelb style decentralization plan, and it is still the most promising logic today.

The best objection has always been that the geography is not so neat. Populations are intermingled. If decentralization gets out of control and national boundaries are erased, then you could see ferocious wars over resources and national spoils.

That’s all true, but separation and containment are still the least terrible of the bad options. The U.S. could begin by arming Iraqi Sunnis directly and helping Sunnis take back their own homeland from the terrorists, with the assurance that they could actually run the place once they retook it.