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"Civil war" is being invoked as a kind of trump card in the debate about U.S. policy in Iraq, both by those who support the continued presence of U.S. forces, as well as those advocating withdrawal. President Bush and his supporters say that U.S. forces bolster Iraq's stability and that a retreat from the country--a strategy some call "cutting and running"--will hasten a descent toward civil war. Egyptian President Hosni Mubarak recently advanced this argument and warned that Iraq is "almost" in civil war already. Others counter that the presence of foreign troops inspires much of the bloodshed, and that the best way to brake the momentum toward civil war is to withdraw them.

Still others, like former interim Iraqi Prime Minister Ayad Allawi, have argued that civil war has already begun. Though he later retreated (somewhat) from this claim, a majority of Americans surveyed have told pollsters they think such a conflict is likely. Yet very few of those who use the term "civil war" ever detail precisely what it would or does mean. All sides look at the disorder and confusion and find the image that best serves their political purposes. But to properly evaluate the wisdom of maintaining the U.S. troop presence, a clear definition is essential.

What Civil War Means

Civil war should be taken to mean the outbreak of large-scale, sustained sectarian violence amidst the collapse of central governance. By this definition, civil war has not yet begun. Though Iraq's newly elected leaders took much longer than expected to settle on Nuri al-Maliki to lead the new government, ministries continued to function in the interim. A constitution, though controversial, has been ratified. It is true that sectarian violence has intensified in recent weeks, particularly following the destruction on February 22 of the Shi'a Askariya mosque in Samarra. But that violence is largely limited to Iraq's four most volatile provinces.

But the likelihood of civil war is rising. The fact that Iraq's sectarian divisions prevented elected officials from selecting a prime minister for several weeks--all the country's most influential players have an interest in near-term stability--is not encouraging.

Moreover, the source of future conflict is embedded in the current constitution. Article 11 of the document states: "All that is not written in the exclusive powers of the federal authorities is in the authority of the regions." That formulation will eventually pit the central government against regional powerbrokers in a sectarian scramble for power and influence. In addition, though the constitution stipulates that the country's oil is the property of all Iraq's people, it gives local governments, not Baghdad, the right to bank the revenues that flow from new fields within their jurisdiction. Kurdish officials have already profited from this loophole by cutting a deal with a Norwegian firm to extract and sell the oil found beneath "their" territory. That company has already begun drilling. In addition, current Iraqi law does not bar local officials from upgrading old sites and reclassifying them as new.

Oil remains the lifeblood of Iraq's economy, accounting for about 97 percent of the country's export revenue. That is income the central government will need for the construction of durable institutions. The government also needs to direct some of the revenue toward resource-poor (and already restive) Sunnis. Substantial sums of international aid still bolster Iraq's stability. Without oil revenue and international financial assistance, the central government will lack both the authority and the means to govern Iraq. Nonetheless, as long as the federal government remains weak, it will be unable to credibly threaten either the Shi'as or Kurds into agreeing to such a distribution. Instead, it will have to resort to creating incentives and encouraging compromise--though it is doubtful these tactics will succeed.

For all the bloodshed elsewhere in the country, the Kurdish-controlled northern provinces have remained relatively peaceful. Kurds have established stable political institutions and achieved modest levels of economic prosperity. For the moment, their enclave of stability protects them from the worst of Iraq's violence and eliminates any need to challenge the status quo. But the Kurds will soon face challenges that may involve them more directly in the rest of the country's battles. Gubernatorial elections this November will force Kurdish candidates to offer voters opposing visions of their future. Some of these would-be leaders will make a name for themselves by calling for independence. More pragmatic Kurdish officials will resist this provocation of Shi'as and Sunnis and try to postpone a potentially incendiary 2007 referendum on the final status of the oil-rich city of Kirkuk. A constitutional change concerning oil revenue, however, would only contribute to the problem by encouraging the less pragmatic to resist compromise.

Despite all the paeans recited on Iraqi democracy, if Shi'a, Sunni and Kurdish voters decide that their representatives cannot advance their individual interests or safeguard their security, significant numbers of them may look beyond politics for such guarantees. Some Shi'as may turn to militia groups like the Mahdi Army, Sunnis to their own militia leaders or to insurgents, and Kurds to those pushing hardest for independence.

Moreover, since the destruction of the Askariya mosque earlier this year, hundreds of Sunnis and Shi'as have already died in a series of attacks and reprisals. Tens of thousands more have fled the mixed Sunni-Shi'a regions of their birth, creating artificial ethnic and sectarian partitions that further balkanize Iraqi politics. Sunni and Shi'a militia groups now move freely within their territories, carrying out violent attacks on enemies, real or perceived. The new Iraqi army lacks the muscle to stop them.

The government's limited authority, the growing influence of militia leaders, a durable insurgency, Iran's sway over many Shi'a in Baghdad and the south, and the natural progression of sectarian politics will dangerously destabilize Iraq over the course of this year. The risk is growing that instability will push the country toward civil war.

What A Civil War Looks Like

What would happen if the central government in Baghdad collapses or ceases to function as a viable force? The outlines are pretty clear.

Iraq would be effectively broken into three autonomous regions composed of Shi'a, Sunni and Kurdish interests in the south, center and north of the country, respectively, and pit rival factions within each group against one another. Sectarian fighting would spread through much of Iraq. International reconstruction aid would cease. The White House would face tremendous pressure to quickly withdraw U.S. troops.

Neighboring states would race to fill the power vacuum left by the central government's disintegration. We can expect that Iran and Saudi Arabia would finance warring Shi'a and Sunni militia groups as proxies. And while this may already be occurring to a limited extent, if U.S. troops leave, the problem will grow quickly. Furthermore, if Iraq indeed becomes a regional battleground, simmering Sunni-Shi'a resentments elsewhere in the region could erupt into violent unrest. This would be particularly dangerous for Saudi Arabia, where minority Shi'a are concentrated along the border with Iraq in the country's Eastern province, where most Saudi oil is produced. Also at risk are Lebanon and Kuwait (home to sizable Shi'a minorities) and Bahrain (a majority-Shi'a state ruled by a Sunni monarchy). An Iraqi civil war could destabilize the Jordanian monarchy as well, as refugees surge across the border and overwhelm the country's ability to cope. Iraqi Kurds might flee into neighboring Iran, as hundreds of thousands did in 1991 when faced with attacks from Saddam. Their presence could spark unrest in Iran's own Kurdish regions. With a rise in regional tensions, we should expect a spike in military spending throughout the Middle East.

But we should avoid the temptation of assuming that a civil war in Iraq would be the equivalent of Armageddon or that a civil war would be the worst of all possible outcomes.

First, even civil war would not shut in all of Iraq's oil. Yes, new investment in energy would dry up, because there would be no central authority to enforce the laws and regulations that regularize business operations--and no single military authority capable of protecting oil infrastructure. The pipeline that moves oil from the Kurdish provinces into Turkey has already sustained considerable damage and remains vulnerable to any surge in fighting.

But nearly two-thirds of Iraq's current production, located in the Shi'a-dominated south, would probably continue to flow. Shi'a forces are likely to be better armed and equipped than other groups to fend off insurgent attacks. Aid from Iran would help preserve that advantage. It would be difficult for Sunnis from central Iraq to infiltrate the south of the country, because regional accents are easily detectable and vigilance against Sunni attacks there would remain high. There are still many Sunnis living in the southern provinces, but those who remain there once sectarian violence began would be unlikely to risk reprisal for attacks on Shi'a property. Over time, the inability to maintain and upgrade oil infrastructure would take a toll. But even in a worst-case civil war scenario, the southern provinces could probably provide international markets with more than one million barrels of oil per day for the near future.