How did the Iraq War end?

 How did the Iraq War end? A. American forces negotiated a withdrawal with the Iraqi government so they could focus on fighting the war in Afghanistan, B. American forces negotiated a withdrawal with the Iraqi government after the U.S. had effectively won the war, C. American forces were forced out of Iraq by insurgent groups who gained control of the nation's government, or D. American forces negotiated a withdrawal with the Iraqi government while the nation still struggled to maintain order.