Going out of Iraq

Now that Americans seem to agree that the military intervention in Iraq was a bad idea (or that it was a good one but poorly implemented), they must still decide how to get out.

They could leave the country to the ruling Shia militia men, and look away while Sunni get slaughtered. After all, what can one do about such barbaric behaviour?

I'm being cynical here, there must be better solutions. I see only one viable option. How is the current situation? Kurdistan looks OK, if you don't see Kurdish militias chasing away Sunni settlers from Mosul as a problem. Close ties between Kurdish leaders and Americans mean it's possible to pressure Kurdish militias to behave. The Shia south suffers from Sunni terrorists, but Shia militias should be capable of keeping car bombings in (relative) control. They get unlimited supplies from Iran, so their survival as a people should not be endangered.

Remains Baghdad and Sunni areas. It is now clear that a united democratic Iraq is not going to happen. Americans should aim divide the country, and prevent ethnic cleansing. That can be achieved through massive increase in military presence on the ground. The idea is to extend the green zone to the entire city. Being no military expert, I have no idea if that's feasible. If not, another option is to divide Baghdad in respectively Sunni and Shia quarters and strongly advise inhabitants to move out to their assigned areas. I know that is basically what ethnic cleansing is all about, but if it cannot be avoided, one should aim to achieve the same results with as little life loss as possible.