4) Shia Dictatorship: Shia Arabs win the chaotic battle of neighborhoods, forcing Sunni Arabs to flee. Call it "de facto" ethnic cleansing, as the Sunnis flee to Sunni states, or move to the United States. Al-Qaida, however, retains a presence. A hard-line Shia regime takes power in Baghdad with the mission of eradicating al-Qaida. The Kurds retain a high degree of autonomy with just enough connection to Baghdad to keep the Turks away.

5) "Gang Up":  A calculated version of Scenario 4 -- Rwanda in the desert. Shia Arabs and Kurds launch a coordinated campaign to eliminate Iraq's Sunni Arab community. The threat of Iranian intervention prevents Sunni Arab nations from protecting Iraqi Sunnis.

6)  Chaos: Iraq shatters into ethnic enclaves, with a few "new Mesopotamian city states" managing to control oil fields. Iran and Turkey exert "regional influence" over eastern and northern Iraq, respectively, but concerned about confrontation between themselves or provoking sanctions from Europe and the United States, neither sends its military forces in large numbers beyond current borders.

Terror attacks and intermittent fighting afflict neighborhoods throughout Iraq. Local warlords rule by fear and make money by either smuggling oil, drugs or arms. This tribal hell is a perfect disaster -- the kind of disaster that allows al-Qaida to build training facilities and base camps for operations throughout the Middle East and Europe.

7)  The Iraqi Center Holds: The democratic government proves to be resilient. The assumption behind this scenario is that Iraq's government is just responsive enough and its security forces are just strong enough to withstand attacks by extremists and give Iran pause. After several months of brutal warfare, the Iraqi Army destroys insurgent groups. Out of seven "rapid withdrawal" scenarios only one -- number seven -- clearly benefits the majority of Iraqis.