Can Iraq hold together? It’s worth examining what is happening in that country through a broader prism. If you had looked at the Middle East 15 years ago, you would have seen a string of strikingly similar regimes — from Libya and Tunisia in the west to Syria and Iraq in the east. They were all dictatorships. They were all secular, in the sense that they did not derive their legitimacy from religious identity. Historically, they had all been supported by outside powers — first the British and French, then the superpowers — which meant that these rulers worried more about pleasing patrons abroad than currying favor at home. And they had secure borders.

Today, across the region, from Libya to Syria, that structure of authority has collapsed and people are reaching for their older identities — Sunni, Shiite, Kurd. Sectarian groups, often Islamist, have filled the power vacuum, spilling over borders and spreading violence. In Iraq and elsewhere, no amount of U.S. military power can put Humpty Dumpty back together.

There are exceptions. Algeria remains an old-fashioned secular dictatorship. Egypt, perhaps the longest-functioning state in the world, has reasserted the old order by using force. The Gulf monarchies — Saudi Arabia, Kuwait, the United Arab Emirates — have withstood the turmoil partly because of greater legitimacy and mostly because of massive patronage systems. And most hopefully, Morocco, Jordan and Tunisia have reformed enough to keep revolutionaries at bay.

The old order was probably unsustainable. It rested on extreme suppression, which was producing extreme opposition movements, and on superpower patronage, which couldn’t last. The countries with significant sectarian divides and in which minority groups ruled — Iraq and Syria — became the most vulnerable.

Let’s be clear. The Iraq war was the crucial trigger, and the U.S. occupation needlessly exacerbated sectarian identities rather than building national ones. But once the old order broke, Iraq’s Shiites, who had been suppressed for decades, in some cases brutally, were not likely to sign up to share power easily with their former tormentors.

Iraqi men brandish their weapons as they show their willingness to join Iraqi security forces in the fight against Jihadist militants who have taken over several northern Iraqi cities on June 19, 2014, in the southern city of Basra. (Haidar Mohammed Ali/AFP/Getty Images)

During and immediately after the surge — 2007-08 — Prime Minister Nouri al-Maliki behaved differently. But if it took the danger of civil war, the presence of about 200,000 foreign troops, a particularly skilled American general (David Petraeus) and billions of dollars to force him to make nice for a brief while, it was unlikely to be a long-term arrangement.

It is doubtful that a Shiite government in Baghdad — using an increasingly Shiite army to defend itself — will ever fully regain the allegiance of the Sunnis. The Sunnis have done enough killing to keep the Shiites wary for decades. Washington has urged the Baghdad government to be inclusive. It has hinted that the best outcome would be a new Iraqi government with a broad coalition. That’s true, but it’s also unlikely. Washington needs a Plan B.

Plan B should be an enclave strategy. The United States should recognize that Iraq is turning into a country of enclaves and work to ensure that these regions stay as stable, terrorism-free and open as possible. The Kurdish enclave, bolstered by having captured the vital city of Kirkuk, is already a success story. The Shiite region of the south can be stable. It will be possible to work with countries such as Saudi Arabia and Jordan to influence the Sunni groups in the middle of the country, purging terrorists and empowering moderate Sunnis.

A comparable strategy in Syria would allow groups such as the Kurds and Sunnis to protect their own areas from Bashar al-Assad’s brutality but recognize that they will not be able to topple the regime. There will be places where the Islamic State of Iraq and Syria (ISIS) and similar groups gain strength. In those areas, Washington would have to use drones, counterintelligence and occasional Special Operations forces strikes — just as it does in Afghanistan, Pakistan, Yemen and Somalia. The world of enclaves already exists. Washington simply has to realize that parts of Iraq are now in it.

The polyglot Middle East has been dying for a while, but it is now on its last legs. Countries rich in minorities, such as Iraq, have seen their Christian populations flee or be massacred. Where minorities remain, communities are segregating themselves.

The United States can’t stop a tidal trend. What it can do is try to limit the fallout, bolster stable countries and zones, support those who believe in reconciliation, and protect itself and its friends.

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