Although it was certainly not his intention, George W. Bush broke up Iraq when he ordered the invasion in 2003. The United States not only removed Saddam Hussein, but it also smashed, and later dissolved, the institutions that enabled Iraq's Sunni Arab minority to rule the country: the army, the security services and the Baath Party. Kurdistan, free from Hussein's rule since 1991, moved to consolidate its de facto independence. Iraq's Shiites, suppressed since the founding of the Iraqi state, have created a theocracy in southern Iraq and have no intention of allowing a central government in Baghdad to roll it back. Iraq's new constitution merely ratifies this result.

There is no reason to mourn the passing of the unified Iraqi state. For Iraq's 80-year history, Sunni Arab dictators held the country together -- and kept themselves in power -- with brutal force that culminated in Hussein's genocide against the Kurds and mass killings of Shiites. As a moral matter, Iraq's Kurds are no less entitled to independence than are Lithuanians, Croatians or Palestinians. And if Iraq's Shiites want to run their own affairs, or even have their own state, on what democratic principle should they be denied? If the price of a unified Iraq is another dictatorship, it is too high a price to pay.

Iraq's Kurds, Shiites and Sunni Arabs do not share the common values and aspirations that are essential to building a unified state. The country's Kurds are avowedly secular and among the most pro-American people in the world. Almost unanimously they want nothing to do with Iraq. Iraq's Shiites, whether we like it or not, have voted overwhelmingly for pro-Iranian religious parties. Iraq's Sunni Arabs, through their own choice, boycotted the constitutional assembly. Some of the leaders who claim to speak for the Sunnis say they want a unified state, though it seems their real concern is that they no longer rule Iraq. Even if it had been done competently, American-led nation-building could not overcome these divisions.

The constitution accommodates all three groups. Each can have its own region. Except for a few matters in the exclusive jurisdiction of the federal government, regional law prevails. Thus Kurdistan can continue to be secular while the Shiites can create an Islamic state in southern Iraq if their constituents so choose. Regions can have their own militaries and control part of their water and oil resources.

Logic would suggest that once they come to terms with the fact that they no longer rule Iraq, the Sunni Arabs will realize that the constitutional framework actually protects them from domination by the Shiite majority. It does not leave the Sunni Arabs penniless as some fear; they get a proportionate share of Iraq's oil revenue. But Kurdistan and the Shiite south will manage new oil fields in their own regions. When the Sunni Arabs were in charge, they used Iraq's oil to finance their own development -- and the destruction of Kurdistan and the south. The Kurds and Shiites will not let this happen again.

The United States should focus now not on preserving the unity of Iraq but on avoiding a spreading civil war. The constitution resolves the issues of oil, territory and control of the central government that might intensify conflict. Engaged diplomacy will be required to make these provisions work, especially with regard to the territorial dispute between Kurdistan and Arab Iraq over the ethnically mixed province of Kirkuk. A referendum will decide its status by Dec. 31, 2007. Meanwhile, the United States should promote a special regime for Kirkuk with entrenched power-sharing for all communities, so as to make the referendum's outcome as painless as possible for the losers.

Iraq's political settlement can pave the way for a coalition exit. Foreign forces have no security role in Kurdistan and only a minimal one in the south. In the Sunni areas, the focus should be on developing a regional army that is aligned with moderate political elements. While the Bush administration pretends there is an Iraqi army today, it actually consists of homogenous Kurdish, Shiite or Sunni Arab battalions loyal not to the civilian authorities in Baghdad but to their respective communities.

It is hard to win hearts and minds in the Sunni Arab areas when the Iraqi troops fighting there are seen not as fellow citizens but as alien Kurds and Shiites. There are tribes and other Sunni Arabs willing to fight the terrorists, but not as collaborators. The coalition could base its forces in Kurdistan, where the population would welcome them and where they can be ready to move in case the Sunni Arab military proves unable or unwilling to take on the terrorists.

As Iraq divides, the problem of Baghdad becomes central. Religiously and ethnically mixed, Baghdad is already the front line of the sectarian war between Sunnis and Shiites. Kurdistan's departure from Iraq -- which seems inevitable in the not-too-distant future -- will not greatly affect the city, but the separation of Sunni Arabs and Shiites into independent states would cause havoc. Fortunately, this is much less likely, especially if federal arrangements work.

As Yugoslavia broke up in 1991, the first Bush administration put all its diplomatic muscle into a doomed effort to hold the country together, and it did nothing to stop the coming war. We should not repeat that mistake in Iraq.

The writer, a former U.S. ambassador to Croatia, is senior diplomatic fellow at the Center for Arms Control and Non-Proliferation. He has advised Kurdish leaders.