structural:summarization
Iraqi Insurgency (2003–11)

However, an insurgency arose against the U.S.-led coalition and the newly developing Iraqi military and post-Saddam government. The rebellion, which included al-Qaeda-affiliated groups, led to many coalition casualties. Other elements of the insurgency were led by fugitive members of President Hussein's Ba'ath regime, which included Iraqi nationalists and pan-Arabists. Many insurgency leaders were Islamists and claimed to be fighting a religious war to reestablish the Islamic Caliphate of centuries past. Saddam Hussein was captured by U.S. forces in December 2003 and was executed in 2006.

In 2004, the insurgent forces grew stronger. The U.S. launched offensives on insurgent strongholds in cities like Najaf and Fallujah.

In January 2007, President Bush presented a new strategy for Operation Iraqi Freedom based upon counter-insurgency theories and tactics developed by General David Petraeus. The Iraq War troop surge of 2007 was part of this "new way forward", which along with U.S. backing of Sunni groups it had previously sought to defeat has been credited with a widely recognized dramatic decrease in violence by up to 80%.

The war entered a new phase on 1 September 2010, with the official end of U.S. combat operations.