"Operation Iraqi Freedom overthrew Saddam Hussein's regime, but much of Iraq remains violent because of Sunni Arab resentment and a related insurgency, compounded by Sunni-Shiite sectarian violence and increased violent competition among Shiite groups as well. Compounding the internal violence is growing tension on Iraq's northern border with Turkey; the north has been the one area of Iraq to experience peace and relative prosperity since the U.S. intervention in 2004. Mounting U.S. casualties and financial costs -- without clear movement toward national political reconciliation among Iraq's major communities -- have intensified a debate within the United States over whether to reduce U.S. involvement without completely accomplishing initial U.S. goals."
CRS Report for Congress, RL31339