Army Col. Joel Rayburn, a senior research fellow at the National Defense University, is a historian who served as an adviser to Gen. David Petraeus in Iraq. He is the author of “Iraq After America: Strongmen, Sectarians, Resistance.” The views he expresses here are his own and do not necessarily represent those of the Department of Defense.

Nouri al-Maliki may have agreed to step down as prime minister of Iraq on Thursday, but the damage he has wrought will define his country for decades to come. The stunning collapse of the Iraqi state in its vast northern and western provinces may be Maliki’s most significant legacy. After nine decades as the capital of a unitary, centralized state, Baghdad no longer rules Kurdistan, nor Fallujah, nor Mosul, and might never rule them again.

To his likely successor, Haider al-Abadi, Maliki will bequeath an Iraqi state that has reverted to the authoritarian muscle memory it developed under Saddam Hussein. But it will be a state that effectively controls not much more than half the territory Hussein did. As Maliki and his loyalists succeeded in consolidating control of the government and pushing rivals out of power, they drove the constituencies of those they excluded — especially Sunni Arabs and Kurds — into political opposition or armed insurrection. Their drive for power alienated Iraqis across all communities from the central state whose wards and clients they had once been, leaving almost no provincial population trustful of the central government. Maliki has held sway in Baghdad, but whole swaths of Iraq have fallen out of his control: The tighter he grasped the state, the more the country slipped through his fingers.

The current crisis in Iraq goes far beyond the question of who will lead the next government in Baghdad. Iraqis have entered into a civil war whose logical conclusion is the breakup of the country. What we are witnessing in Iraq today is the beginning of a process that could become at least as destructive and bloody as the breakup of Yugoslavia. The longer it is allowed to unfold, the less likely it will be stopped, and the more likely it will spill over on a large scale to destabilize the surrounding region.

It is tempting to conclude that the U.S.-led regime change of 2003 inevitably led to sectarian violence and politics in Iraq by opening up the country’s preexisting fractures. But the deep sectarianism of the past decade was neither foreordained to follow Hussein’s fall nor completely natural in Iraqi society. It was instead a calculated objective of the powerful, mainly expatriate parties that arrived in Baghdad after April 2003, bringing with them sectarian agendas that had been decades in the making. These groups, which included Maliki and the Dawa party , as well as almost all of Iraq’s major Islamist and ethnic parties, have had independent but complementary interests in polarizing the country, turning a mixed-sect, multiethnic nation into one of homogeneous ethnic and sectarian political constituencies. The result has been a devastating civil war, and an Iraq more thoroughly sorted by sect and ethnicity than ever before.

As Iraq’s major parties have carved the nation into political empires, they have in many regions allowed the state to recede from the streets, creating power and security vacuums that militant and criminal groups have been quick to fill. The creeping takeover of Sunni neighborhoods by Islamic State fighters and their fellow travelers has been well documented, but in other areas Shiite Islamist militants have roamed freely for years, with the state absent or complicit. Away from the Islamic State’s atrocities in the far north, Shiite militant groups trained by Iran to fight U.S. troops until 2011 now seem poised to insulate Baghdad and the Shiite south from the Islamic State threat. They eventually may evict Sunnis from the region around Baghdad in the name of counterterrorism, with the assistance of the Iranian regime and Lebanese Hezbollah, and with the political blessing of the Shiite Islamist political parties that on Monday nominated Abadi as their premier.

For years now, some outsiders and some Iraqi factions have called for the partition of the country as a matter of policy — a solution to the intractable political disputes. Perhaps the best-known instance was in 2006, when then-Sen. Joe Biden and Leslie Gelb of the Council on Foreign Relations called for the division of the country into three autonomous regions, based on sect, with a central government that would “control border defense, foreign affairs and oil revenues.” Invoking the example of Bosnia, Biden and Gelb offered their plan as a way to keep the country intact and prevent sectarian warfare from escalating.

But as we are likely to find out in the coming years, there is no way for Iraq to be divided into three homelands for Shiites, Kurds and Sunnis without experiencing exactly the massive human misery that Biden, Gelb and others hoped partition might forestall. No clean ethno-sectarian lines already exist in Iraq, meaning that the boundaries of the various statelets would have to be fought over. The populations of northern and central Iraq in particular are so intertwined that separating people into sectarian enclaves would immediately prompt violent sectarian cleansing on a scale sure to exceed that of Yugoslavia. At least a quarter of a million non-Sunnis would probably be forced to leave Sunni-majority territories, while more than half a million Sunnis would probably be expelled from the greater Baghdad region, with those Sunni Baghdadis that remain herded into ghettos in and around the city.

There would also be millions of Iraqis caught in limbo. What would become, for example, of the large minority population that is not Sunni, Shiite or Kurd? And what would become of Iraq’s more than 1 million Turkmen? What would become of the millions of Iraqis in intermarried families of Shiite and Sunni or Arab and Kurd? The fragmenting of the country into sectarian cantons would leave these millions with no clear place to go.

Nor is it likely that the fragmentation of Iraq, once begun, would stop at just three sections. The country would be far more likely to split effectively into four pieces or more. The Sunnis of Anbar and Mosul, who have a long-standing rivalry, would be unlikely to consent to living together in one Sunnistan, where one region might be dominated by the other. They would be more likely to live in competing Tigris and Euphrates regions or statelets. Nor is it clear that, once unmoored from Baghdad, the major Kurdish parties would live together in one region where one party could rule the others. Lastly, the shrunken Shiite-majority section would be a rump Iraq stretching from Samarra to the Persian Gulf, rich in oil but certain to fall into the Iranian regime’s orbit for the foreseeable future.

Nor would the creation of these sections be the end of the matter, as then-Deputy Prime Minister Saleh al-Mutlak, a Sunni, warned in a 2011 CNN interview: “Dividing the country isn’t going to be smooth, because dividing the country is going to be a war before that and a war after that.” The new states or quasi-states of the former Iraq would surely enter into a long series of wars that none would be strong enough to decisively win, with a death toll unlikely to be less than the roughly quarter-million killed in the Yugoslav wars and a total displacement of perhaps one-quarter of Iraq’s population.

If Iraq fragments in this manner, either formally or de facto, there will be no way to preserve a meaningful central structure in which the different sectarian enclaves together defend the country’s borders and share natural resources. In the north in particular, Sunni Arabs, Turkmen and Kurds are more likely to war over the oil-rich disputed territories, while the governments in Baghdad and Irbil will never share oil revenue with Sunni provinces that are at war with the Shiites and Kurds. And since there are no bodies of water or mountain ranges separating Iraq from its western and southern neighbors, these conflicts will not be physically contained as the Balkan wars were. They are sure to spill over, eventually drawing in every neighbor even more deeply than they are already.

Iraqi leader Nouri al-Maliki announced on Thursday that he is dropping his bid for a third term as prime minister and pledged support for his replacement, Haider al-Abadi. (Reuters)

Iraq’s prospects for political stability are dim, and the country faces fundamental questions that Maliki’s impending departure will do little to solve. Reintegrating the Sunni community and provinces back into the Iraqi state would be the necessary starting point for leaders who wish to preserve their country. But the political environment that Maliki will leave behind is largely devoid of the trust necessary for partnerships and power-sharing. One reason Maliki and his allies have mightily resisted leaving power is that after eight years of rough rule, no member of his group can be fully assured that a successor party will leave them to live in peace. Similarly, what Kurdish leader believes that Sunni Arabs, if ever back in power, would not immediately attempt to push the Kurds back into the mountains and crush Kurdish nationalism? And after a decade of attempting to make Sunnis a permanent minority underclass, what Shiite supremacist does not fear what Sunnis would do if they ever regained control of Baghdad?

The enduring dilemmas that have dogged modern Iraq — the relationship between the people and the state, the relationship between Kurdistan and Arab Iraq, the relationship between Sunnis and Shiites, the relationship between Baghdad and its 18 provinces — remain unsettled. It would take a leader or movement of extraordinary vision to settle them peacefully, and no such visionary is on the horizon. It is Iraq’s strongmen, sectarians and Islamist resistance who control the path to conflict resolution. The longer they hold sway, the smaller the chance that Iraq will hold together.

It is not too late for Iraq. But soon, it will be. The civil war of the past decade has been many things: a struggle between terrorists and the state, between religious extremes, between Maliki loyalists and their rivals, between regional proxies, between sects and ethnicities that have not relearned how to coexist. But it has most essentially been a war on Iraqi society itself, slowly draining the lifeblood of one of the world’s oldest countries, which after five millennia has begun to expire before our eyes.

Twitter: @joel_rayburn

Read more from Outlook:

Why we stuck with Maliki — and lost Iraq

Five myths about the Islamic State

Why Obama should send several thousand U.S. troops back to Iraq

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