Iraqi insurgency (2003–2011)

The Iraqi insurgency lasted from 2003 until 2011, beginning shortly after the 2003 American invasion deposed longtime leader Saddam Hussein, and lasting until the end of the Iraq War and U.S. withdrawal in 2011. It was followed by a renewed insurgency.

The initial outbreak of violence (the 2003–2006 phase) was triggered by the fall and preceded the establishment of the new Iraqi government by the Multi-National Force – Iraq (MNF–I), which was led by the U.S. From around 2004 to May 2007, Iraqi insurgents largely focused their attacks on MNF-I troops, but later shifted to targeting the post-invasion Iraqi security forces as well.

The insurgents were composed of a diverse mix of private militias, pro-Saddam Ba'athists, local Iraqis opposed to the MNF–I and/or the post-Saddam Iraqi government, and a number of foreign jihadists. The various insurgent groups fought an asymmetric war of attrition against the MNF–I and the Iraqi government, while also fighting among themselves.

The insurgency was shaped by sectarian tensions in Iraq, particularly between Shia Muslims (~60% of the population) and Sunni Muslims (~35% of the population). By February 2006, the violence escalated into a Shia–Sunni civil war, and for the next two years, the MNF–I and the Iraqi government were locked in intense fighting with various militants, who were also targeting each other based on their sectarian affiliations. Many of the militant attacks in American-controlled territories were directed at the Shia-dominated government of Nouri al-Maliki. Militancy continued amid post-invasion Iraqi reconstruction efforts, as the federal government tried to establish itself in the country. The civil war and sectarian violence ended in mid-2008, having been quelled by the American troop surge of 2007.

However, after the American withdrawal from Iraq in December 2011, a renewed sectarian and anti-government insurgency swept through the country, causing thousands of casualties. Two years later, the violence of the new insurgency escalated into the Second Iraq War, largely triggered by the rise of the Islamic State.