Barry Posen makes a strong case for the withdrawal of American troops from Iraq. His main point, now widely agreed upon even in Washington, is that the American military presence is motivating the insurgency and generating a steady supply of recruits from inside and outside Iraq. Like the other “national liberation” insurgencies of the past century, this form of guerrilla war cannot be won by the imperial invaders. The theory is that if American troops pull out, the insurgency will collapse and the United States will have achieved its goal.

It will be a pullout that leaves Iraq in a far better state than it is today or will be for the foreseeable future under continued U.S. military occupation.

The main problem, however, is that no one knows whether the insurgency will be replaced by an equally vicious, or perhaps even more bloody and protracted, civil war between Iraqi Sunnis and Shias. Posen argues that since the majority Shias run the government and armed forces and control all the heavy military equipment in the country, they should be able to prevent the Sunnis from running amok. Once American troops are gone, however, the Sunnis may gain support from their Arab Sunni neighbors, notably Saudi Arabia and Syria, whose greatest fear is that Iraqi Shias will join with Iranian Shias to form a wealthy, industrially advanced new Persian empire. Moreover, as Posen notes, most Arab countries are tightly controlled monarchies. They may view a stable, pluralistic democratic government in Iraq as a bad precedent—and an ongoing civil war as a useful diversion from internal pressure for reform.

Posen’s solution is to create a loose federation of three self-governing regions, run by the Kurds in the north, the Sunnis in the west, and the Shias in the center and south. In effect, Posen’s message to the Bush administration is that the way to create a modicum of peace with political progress in Iraq is to press the Shias to offer considerable political independence to the Sunnis, comparable to that exercised by the Kurds for almost 15 years.

In this regard, I think Posen is exactly right. The solution, as always for civil wars based on ethnicity or religion, is not military but political. An effort to “win” militarily—that is, to keep American troops fighting until we see an end to all suicide bombings, improvised explosive devices, and other forms of armed resistance—will only lead to more Iraqi death and suffering, and more American troops dead or maimed.

This leaves the questions of how and when American troops should pull out, and how a functioning Iraqi federation might be established. Posen does not give a reason for choosing 18 months rather than 24, 12, six, or three. Taken alone, the view that the American presence is leading to greater bloodshed than would occur after withdrawal suggests that the quicker the withdrawal, the better. But there are other important factors to consider: Iraq needs a viable constitution that confers substantial self-governance on the Sunnis, as well as some form of revenue-sharing from the oil fields, which lie entirely within the regions that will be controlled by the Kurds and the Shias.

Posen suggests that 18 months are needed for training Shia troops. I cannot see how another 18 months will do what the last 24 months have failed to accomplish, or how training Shia troops is crucial to the establishment of a modus vivendi between the Shias and the Sunnis. The goal is not to have Shia armed forces perform functions comparable to those now being carried out by American troops; the goal is to eliminate the need for anti-insurgency fighting, thus reducing demands on the Shia-led government, armed forces, and police to normal intra-state functions.

To begin handing over responsibility to the Shias for maintaining an interim government and for shaping a viable constitution, President Bush should announce the following revamped policy for Iraq: First, the United States supports the creation of a federation of three self-governing regions and expects nearly all the bloodshed to end when this is accomplished and the American troops are gone. Second, American troops will begin a gradual pullout now, while Iraqis work out their political future. Third, the pace of the American withdrawal will inversely match progress toward the creation of a viable federation. If steady progress is being made, the pullout might be spread over a year, but if no progress is being made, the pullout will be more rapid, possibly completed in six months. Either way, the rate of withdrawal must allow a reasonable period of time for the additional political negotiations needed to establish a federated form of government.

Announcing support for a federation and imminent withdrawal will take the wind out of the sails of the fighters. Announcing the inverse rate of withdrawal will put additional pressure on the Shias to come up with a political solution acceptable to Sunni leaders This will not be an unconditional pullout that would lead to civil war and concede victory to the insurgents. It will be a pullout that leaves Iraq in a far better state than it is today or will be for the foreseeable future under continued U.S. military occupation.