[A]ren't the American soldiers there to stop sectarian violence -- to stop Iraqis from killing each other?
Colonial powers, when they take over a foreign land, can keep the remaining power structure, as the British did in Iraq by ruling though the Sunnis, or they can upset the existing order and empower the previously down trodden, as the Americans did with the Shia.
In America's case, the United States now doesn't like what it wished for, and has decided to fight both the Sunni insurgents and the Shia militias, inserting itself into a civil war.
'Surge' doomed to final failure (by H.D.S. Greenway, Boston Globe - 3.13.07)
at 11:26 AM