American casualties went up again in August, to 620 (13 percent dead), not quite the level of two months ago, but higher than July.  Iraqi police and army casualties were three times the American level. This reflects the higher number of Iraqi security troops in action. Another factor is the increased activity, by security forces, in Sunni Arab areas. This has forced Sunni Arab tribes to take sides. Either go with the government, or gather the tribal militia and fight. The tribes that fight are taking a beating. While they can often drive away Iraqi police or troops, if the Americans show up, it's the tribal gunmen who have to flee or die. Increasingly, the Iraqi forces go into action with an American air controller team in tow. This means that they can call in U.S. smart bombs. That makes a big difference. Unlike the al Qaeda terrorists, most Sunni Arab tribal gunmen are not eager to be "martyrs." And they know how the smart bombs work. There's no defense against the smart bombs. Iraqi commanders can often get the tribal leaders to cooperate by simply pointing a finger skyward. 

Some Sunni Arab tribes are determined to fight, believing that they will lose forever the power and wealth they had when the Sunni Arabs ran the country. But these tribes comprise only a few percent of the population. Some Kurdish and Shia Arabs favor driving these tribes out of the country, into Syria, Jordan or Saudi Arabia. Those three countries have long feared this kind of ethnic cleansing, but are not willing to go to war over the issue. Other Sunni Arab tribes will fight, but eventually settle after they have taken a beating. The government does not support the ethnic cleansing approach, so the battles in western Iraq go on.

Ethnic cleansing is nothing new in Iraq. Even before Saddam Hussein, tribal conflicts often led to ethnic groups being forcibly moved out of their home areas. Saddam Hussein, however, did it on a large scale, forcing hundreds of thousands of Kurds out of oil rich areas around Kirkuk. These Kurds are now returning, and forcing out the Sunni Arabs who replaced them over the last two decades.