"As best I can piece it together, what actually seems to have happened was that the escalation troops began by disarming the Sunni Arabs in Baghdad. Once these Sunnis were left helpless, the Shiite militias came in at night and ethnically cleansed them. Shaab district near Adhamiya had been a mixed neighborhood. It ended up with almost no Sunnis. Baghdad in the course of 2007 went from 65 percent Shiite to at least 75 percent Shiite and maybe more. My thesis would be that the United States inadvertently allowed the chasing of hundreds of thousands of Sunni Arabs out of Baghdad (and many of them had to go all the way to Syria for refuge). Rates of violence declined once the ethnic cleansing was far advanced, just because there were fewer mixed neighborhoods."