In 2006, Joe Biden, Les Gelb and many others proposed plans to decentralize power in Iraq. Biden, then a United States senator from Delaware, Gelb and others recognized that Iraqi society was fracturing into sectarian blocs. They believed that governing institutions should reflect the fundamental loyalties on the ground. According to the Biden plan, the central Iraqi government would still have performed a few important tasks, but many other powers would have been devolved to regional governments in the Sunni, Shiite and Kurdish areas.

The administration of George W. Bush rejected that federalist approach and instead bet on a Baghdad-centric plan. The Iraqi prime minister at the time, Nuri Kamal al-Maliki, and his band of Shiite supremacists enflamed sectarian tensions even more, consolidated power, excluded rivals, alienated the Sunnis and Kurds and drove parts of the opposition into armed insurrection.

The Obama administration helped oust Maliki and replace him with a group of more moderate and responsible leaders. But that approach is still centralized and Baghdad-focused. The results are nearly as bad. The Sunnis continue to feel excluded and oppressed. Faith in national institutions has collapsed. Sectarian lines are hardening. Over the last several years, the number of people who tell pollsters that they are Iraqis first and foremost has plummeted.

Vastly outnumbered fighters for the Islamic State keep beating the Iraqi Army in places like Ramadi because the ISIS terrorists believe in their lunatic philosophy while the Iraqi soldiers no longer believe in their own leadership and are not willing to risk their lives for a dysfunctional, centralized state.

This attempt to impose top-down solutions, combined with President Obama’s too-fast withdrawal from Iraq, has contributed to the fertile conditions for the rise of ISIS. Obama properly vowed to eradicate this terrorist force, but the U.S. is failing to do so.

That’s largely because, mind-bogglingly, the Iraqi government has lost the battle over the hearts and minds to a group of savage, beheading, murderous thugs. As Anne Barnard and Tim Arango reported in The Times on Thursday, ISIS is hijacking legitimate Sunni grievances. Many Sunnis would apparently rather be ruled by their own kind, even if they are barbaric, than by Shiites, who rob them of their dignity.

The United States is now in the absurd position of being in a de facto alliance with Iranian-backed Shiite militias. Up until now, these militias have plowed through Sunni territory “liberating” villages from ISIS and then, often enough, proceeding to execute the local leaders, loot the property and destroy the towns.

The Obama administration is hoping that these militias will restrain themselves and listen to the central authority. But that would be to defy all recent Iraqi history. The more likely scenario is that the militias will occasionally beat ISIS on a tactical level while making the larger climate even worse.

The centralizing strategy has been a failure. Instead of fostering cooperation, efforts to bring Sunni and Shiite elites together have only rubbed at raw wounds, exacerbated tensions and accelerated the slide toward a regional confrontation. ISIS is now targeting Shiite pilgrims in Saudi Arabia in order to enflame that country and widen the religious war that is brewing across the region.

Iran is sponsoring terror armies across the region and trying to turn Shiite Iraq into a satellite state.

Maybe it’s time to shift course.

A brutalizing dynamic is now firmly in place: Sectarian tension radicalizes the leaderships on both the Sunni and Shiite sides. These radicalized leaders incite bigger and uglier confrontations.

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.