As far as I can tell, however, violence in Iraq fell through 2007 not mainly because of US GI’s but because a Shiite ethnic cleansing campaign chased most Sunnis from mixed neighborhoods.

Prime Minister Nouri al-Maliki had convinced Petraeus to begin with the Sunni armed groups, and to disarm them. Once they were helpless, the Shiite militias like the Mahdi Army went in and ethnically cleansed the remaining ones.

Through 2007 forward, as mixed Sunni-Shiite neighborhoods became more solidly Shiite, the death toll began declining. Angry Shiites who wanted to kill a Sunni would have had to get in their cars and drive for a while to find one.

Petraeus knew about the ethnic cleansing campaign. He was aware that it was creating a new wave of Sunni refugees. But he saw the troop escalation or ‘surge’ as the primary reason for the fall in violence.

Based on this misunderstanding of what had happened in Iraq, Petraeus hoped to do in Afghanistan what he thought he did with Baghdad. Hence the mantra, take clear hold build.

But this kind of counter-insurgency would have required hundreds of thousands of fresh troops. Petraeus didn’t have them. It was a huge endeavor.

It has largely failed, though US politicians and journalists seem reluctant to say so.