This month marks the formal withdrawal of U.S. troops from Iraq, more than eight years after they arrived in 2003. What effect will the departure of the troops have on Iraq, and what are the remaining security concerns in the country? I asked Stephen Van Evera, the Ford International Professor of Political Science and an expert in international relations and security, to assess the situation.

Q. What are the possible effects of the U.S. troop withdrawal from Iraq?

A. We hear two worries about the effects of the U.S. withdrawal. First, some fear that Iraq will fall back into civil war. Second, some fear that Iran will exert dominance over Iraq and use it as a base for making wider trouble.

The first worry is not baseless. U.S. forces have dampened violence in Iraq during the past few years by deterring aggression among the Iraqi factions. Once U.S. forces are gone there will be no “cop on the block” to deter violence. Highlighting this risk, violence has risen in Iraq in recent months as U.S. forces have drawn down. But three developments since 2003 have reduced the risk of another full-scale civil war in Iraq.

First, the fighting since 2003 produced ethnic cleansing. This separated the Iraqi factions. Now they cannot get at each other as easily as before. As a result they don’t fear one another as much as before. The war caused great horrors, but the separation it caused has left the factions less able to hurt each other, hence less fearful of being hurt. Hence the factions can better agree to live and let live.

Second, the stalemate outcome of the war has taught many Iraqis who once sought dominance for their faction that no faction can dominate Iraq, and all factions must instead find a way to live with the others. Specifically, in 2003 some Sunnis thought they could gain political dominance in Iraq by force. They were disabused of this delusion by bitter defeats on the battlefield. Sunni leaders now broadly understand that Sunni hegemony is impossible, and have curbed their aims accordingly. And on the Shia side, the followers of Muktada al-Sadr have also learned on the battlefield that they cannot easily dominate other factions.

Third, the most violent faction in Iraq, al-Qaida in Mesopotamia, has discredited itself by its barbarous conduct. It behaved with great arrogance and cruelty, often committing indiscriminate slaughter when Iraqis refused its demands. This caused a backlash against it. Al-Qaida remains active and has committed substantial mayhem in recent months but its ability to sow havoc has diminished.

For these three reasons — the separation of peoples, a reduction of illusions of dominance on both sides and the self-discrediting of al-Qaida — a renewal of all-out civil war seems unlikely.

But two aspects of the current scene offer grounds for worry. First, it is not clear that Iraqi Prime Minister Nouri al-Maliki is among those who realize that his faction cannot gain dominance. Al-Maliki, who is Shia, has moved in imperious fashion against Sunnis in recent months. His allies tried to remove many Sunni candidates from the election ballot in 2010, and arrested 600 former Ba’athist Sunnis this fall. Al-Maliki will provoke violence if he continues to behave so imperiously. And second, several inflammatory political questions remain unsettled and could be flashpoints for conflict.

Q. What are these unsettled issues?

A. Arabs, Kurds, Turkmen and other groups are locked in a tense conflict to control Kirkuk. Saddam Hussein expelled many Kurds from Kirkuk during his repressions of the Kurds, and imported Arabs to replace them. Now the Kurds want to return, but the Arabs don’t want to leave.

Iraqis have not worked out a consensus on how to share power in the national government. Democracy in a deeply divided multiethnic state such as Iraq requires a power-sharing arrangement, of the sort that Switzerland and Belgium have created. Simple majority rule won’t work. But Iraqi elites have yet to commit to a power-sharing order in principle, or to work out its details.

Iraqis have not yet agreed on how the Iraqi oil industry shall be managed or how Iraqi oil revenues will be shared.

Q. What about the concern you mention of Iranian domination of Iraq?

A. Fears of Iranian domination of Iraq rest on the premise that Iraqi Shia identify so strongly as Shia, and so little as Arabs or Iraqis, that they will accept domination by Shia Iran. In fact, however, Iraqi Shia have a strong identity as Arabs and Iraqis. They have affinity for other Shia, but will not accept Iran or other non-Iraqis as overlords. Iranian dominance of Iraq is not in the cards.