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,^[12] 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.

The 2003 invasion of Iraq (20 March – 1 May 2003) began the Iraq War, or Operation Iraqi Freedom, in which a combined force of troops from the United States, the United Kingdom, Australia, and Poland invaded Iraq and toppled the government of Saddam Hussein within 26 days of major combat operations. The invasion phase consisted of a conventionally fought war which concluded with the capture of the Iraq capital Baghdad by U.S. forces.

Four countries participated with troops during the initial invasion phase, which lasted from 20 March to 15 April 2003. These were the United States (148,000), United Kingdom (45,000), Australia (2,000), and Poland (194). Thirty-six other countries were involved in its aftermath. In preparation for the invasion, 100,000 U.S. troops were assembled in Kuwait by 18 February.^[13] The United States supplied the majority of the invading forces, but also received support from Kurdish irregulars in Iraqi Kurdistan.

The invasion was preceded by an air strike on the Presidential Palace in Baghdad on 20 March 2003. The following day coalition forces launched an incursion into Basra Province from their massing point close to the Iraq-Kuwait border. While the special forces launched an amphibious assault from the Persian Gulf to secure Basra and the surrounding petroleum fields, the main invasion army moved into southern Iraq, occupying the region and engaging in the Battle of Nasiriyah on 23 March. Massive air strikes across the country and against Iraqi command and control threw the defending army into chaos and prevented an effective resistance. On 26 March, the 173rd Airborne Brigade was airdropped near the northern city of Kirkuk, where they joined forces with Kurdish rebels and fought several actions against the Iraqi army to secure the northern part of the country.

The main body of coalition forces continued their drive into the heart of Iraq and met with little resistance. Most of the Iraqi military was quickly defeated and Baghdad was occupied on 9 April. Other operations occurred against pockets of the Iraqi army including the capture and occupation of Kirkuk on 10 April, and the attack and capture of Tikrit on 15 April. Saddam and the central leadership went into hiding as the coalition forces completed the occupation of the country.

On 1 May, an end of major combat operations was declared, ending the invasion stage of the Iraq War and beginning the military occupation period and the Iraqi insurgency against coalition forces.

On 23 May 2003, Iraqi military personnel, police and security services were disbanded per Order 2 of the Coalition Provisional Authority under Administrator Paul Bremer, leaving 400,000 soldiers and officers jobless, providing a ready pool of recruits for Islamist groups and other insurgents that emerged.^[14][15] Furthermore, for 10 months Iraq's borders were left open for anyone to come in without even a visa or a passport.^[16]

The Iraqi insurgency is composed of at least a dozen major organizations and perhaps as many as 40 distinct groups. These groups are subdivided into countless smaller cells. The American Center for Strategic and International Studies (CSIS) estimated that less than 10% of insurgents are non-Iraqi foreign fighters.^[43] According to the Chief of the British General Staff, General Sir Richard Dannatt, speaking in September 2007,

The tactics of the Iraqi insurgency varied widely. The majority of militant elements used improvised explosive devices (IEDs), car bombs, kidnappings, suicide attacks, hostage-taking, shootings, assassinations, ambushes, sniper attacks, mortar and rocket strikes and other types of attacks to target Iraqis and U.S. forces with little regard for civilian casualties.

A single study has compared the number of insurgent attacks in Iraq to supposedly negative statements in the U.S. media, release of public opinion polls, and geographic variations in access to international media by Iraqis. The purpose was to determine if there was a link between insurgent activity and media reports. The researchers' study suggested it may be possible that insurgent attacks spiked by 5 to 10% after increases in the number of negative reports of the war in the media. The authors believed this may possibly be an "emboldenment effect" and speculated that "insurgent groups respond rationally to expected probability of US withdrawal."^[104]

A series of several polls were conducted to ascertain the position of the Iraqi public further on Al Qaeda in Iraq and the U.S. presence. Some polls found the following:

• Polls suggested the majority of Iraqis disapproved of the presence of Coalition forces.^[105]
• A majority of both Sunnis and Shias wanted an end to the U.S. presence as soon as possible, although Sunnis were opposed to the Coalition soldiers being there by greater margins.^[106]
• Polls suggested the vast majority of Iraqis supported attacks on insurgent groups with 80% supporting US attacks on Al-Qaeda.^[107][108]

Directly after the invasion, polling suggested that a slight majority supported the US invasion.^[109] However, polls conducted in June 2005 suggest that there was some sentiment^{[clarification needed]} towards Coalition armies being in Iraq. A 2005 poll by British intelligence said that 45% of Iraqis supported attacks against Coalition forces, rising to 65% in some areas, and that 82% were "strongly opposed" to the presence of Coalition troops.^[110] Demands for U.S. withdrawal were also signed onto by one third of Iraq's Parliament.^[111] These results were consistent with a January 2006 poll that found an overall 47% approval for attacks on U.S.-led forces. That figure climbed to 88% among Sunnis. Attacks on Iraqi security forces and civilians, however, were approved of by only 7% and 12% of respondents respectively. Polls conducted between 2005 and 2007 showed 31–37% of Iraqi's wanted US and other Coalition forces to withdraw once security was restored, and that 26–35% wanted immediate withdrawal instead.^{[112][113][114]}

A September 2006 poll of both Sunnis and Shias found that 71% of Iraqis wanted the U.S. to leave within a year, with 65% favoring an immediate pullout and 77% voicing suspicion that the U.S. wanted to keep permanent bases in Iraq.^[115] 61% approved of attacks on U.S. forces.^[105] A later poll in March 2007^[116] suggested the percentage of Iraqis who approve of attacks on Coalition forces had dropped to 51%. In 2006 a poll conducted on the Iraqi public revealed that 52% of the ones polled said Iraq was going in the wrong direction, and 61% claimed it was worth ousting Saddam.^[112]

Despite a majority having previously been opposed to the US presence, 60% of Iraqis opposed American troops leaving directly prior to withdrawal, with 51% saying withdrawal would have a negative effect.^[117][118]

The most intense Sunni insurgent activity took place in the cities and countryside along the Euphrates river, from the Syrian border town of al-Qaim through Ramadi and Fallujah to Baghdad, as well as along the Tigris river from Baghdad north to Tikrit. Heavy guerrilla activity also took place around the cities of Mosul and Tal Afar in the north, as well as the "Triangle of Death" south of Baghdad, which includes the "-iya" cities of Iskandariya, Mahmudiya, Latifiya, and Yusufiya. Lesser activity took place in several other areas of the country. The insurgents were believed to maintain a key supply line stretching from Syria through al-Qaim and along the Euphrates to Baghdad and central Iraq, the Iraqi equivalent of the Ho Chi Minh trail.^{[needs update]} A second "ratline" ran from the Syrian border through Tal Afar to Mosul.

Although estimates of the total number of Iraqi guerrillas varied by group and fluctuated under changing political climate, some assessments put the present number at between 3,000 and 7,000 fighters, along with numerous supporters and facilitators throughout the Sunni Arab community. At various points, U.S. forces provided estimates on the number of fighters in specific regions. A few are provided here (although these numbers almost certainly have fluctuated):^{[needs update]}

• Fallujah (mid-2004): 2,000–5,000 In a November 2004 operation, the Fallujah insurgency was destroyed or dispersed, but had staged a comeback in 2005, albeit not to former strength, in the course of 2005–2008 the remainder of the insurgency was defeated in Fallujah and the rest of Al-Anbar province.
• Samarra (August 2011): 1,000+
• Baquba (August 2011 ): 1,000+
• Baghdad (August 2011): 2,000+

Guerilla forces operated in many of the cities and towns of al-Anbar province, due to mostly ineffective Iraqi security forces in this area. There was extensive guerrilla activity in Ramadi, the capital of the province, as well as al-Qa'im, the first stop on an insurgent movement route between Iraq and Syria. In 2006, reports suggested that the Anbar capital Ramadi had largely fallen under insurgent control along with most of the Anbar region, and that as a result, the United States had sent an extra 3,500 marines to reestablish control of the region. In the early part of 2007, the insurgency suffered serious setbacks in Ramadi after they were defeated in the Second Battle of Ramadi in the fall of 2006. With the help of the Anbar Salvation Council, incidents fell from an average of 30 attacks per day in December 2006 to an average of fewer than four in April 2007.^[119]

Baghdad was still one of the most violent regions of the country. Even after the 2007 troop surge, more than two-thirds of the violence that took place in Iraq happened in Baghdad, even though the Iraqi Government was in firm control of the entire city.^{[needs update]} Suicide attacks and car bombs were near daily occurrences in Baghdad. The road from Baghdad to the city airport was the most dangerous in the country, if not the world. Iraqi security and police forces had also been significantly built up in the capital and, despite being constantly targeted, had enjoyed some successes such as the pacification of Haifa Street, which, however, subsequently saw a massive surge of insurgent activity.^[120] and after the failed Coalition Operation Together Forward fell under Sunni insurgent control. The U.S. and Iraqi Forces scored many decisive victories in 2007 during the U.S. troop surge, when they launched Operation Law and Order and Operation Phantom Thunder, which broke the back of the insurgency and led to a mass reduction in violence by 80 percent.^{[needs update]}

Intelligence reports suggested that the base of foreign paramilitary operations moved from Anbar to the religiously and ethnically mixed Diyala province.^[when?] By July 2007, Diyala had fallen under almost total Insurgent control, and had become the headquarters for the Sunni-dominated Islamic State of Iraq, which issued a proclamation declaring the regional capital Baqubah its capital.

In response to a law allowing for the partitioning of Iraq into autonomous regions, members of the Mutayibeen Coalition (Khalf al-Mutayibeen^[121]), a coalition of Sunni insurgent groups including al-Qaeda in Iraq, announced the creation of the Islamic State of Iraq encompassing parts of 6 of Iraq's 18 provinces on 15 October 2006.^[121][122] Yet another show of defiance came on 18 October when Sunni fighters brazenly paraded in Ramadi. Similar parades were held two days later in several towns across western Iraq, two of which occurred within two miles of U.S. military bases.

By October 2006, small radicalized militias had seemed to overshadow the larger and more organized Sunni groups which had composed the insurgency previously.^[123] As disagreements emerged in pre-existing groups for reasons ranging from the rift in the Sunni forces between foreign and Iraqi fighters, competition between Mahdi Army and Badr Brigade, and anger over various decisions such as Muqtada al Sadr's agreement to join the political process, dozens of insurgency groups sprung up across the country, though particularly in Baghdad where the U.S. army listed 23 active militias. Residents described the capital as being a patchwork of militia run fiefs. As a result of the insurgency's splintering nature, many established leaders seemed to lose influence.^{[citation needed]} This was particularly illustrated on 19 October, when members of the Mahdi army briefly seized control of Amarah. The attack, while demonstrating the influence of the Madhi army, was believed to have originated as a result of contention^{[needs update]} between local units of the Madhi army and the allegedly Badr brigade run security forces, and the timing suggested that neither Al Sadr nor his top commanders had known or orchestrated the offensive.^[124]

At the height of the war, insurgents launched hundreds of attacks each month against Coalition forces. Overtime, insurgency groups moved to more sophisticated methods of attacks, such as Explosively formed penetrators, and infrared lasers, which could not be easily jammed. These attacks contributed to the rate of civilian casualties, which in turn reduced Iraq's public safety, as well as the reliability of infrastructure.^[125]

As of 29 January 2009 4,235 U.S. soldiers, 178 British soldiers and 139 soldiers from other nations (allied with the coalition) died in Iraq. 31,834 U.S. soldiers had been wounded.^[126] Coalition forces did not usually release death counts. As such, the exact number of insurgents killed by the Coalition or Iraqi forces is unknown. Through September 2007, more than 19,000 insurgents were reported to had been killed in fighting with Coalition forces, and tens of thousands of Iraqi "suspected civilians" were captured (including 25,000 detainees in U.S. military custody at the time), according to military statistics released for the first time.^{[127][needs update]}

Over 500 counterinsurgency operations were undertaken by the U.S.-led Coalition or the Iraqi government. These included Operation Option North and Operation Bayonet Lightning in Kirkuk, Operation Desert Thrust, Operation Abilene and Operation All American Tiger throughout Iraq, Operation Iron Hammer in Baghdad and Operation Ivy Blizzard in Samarra – all in 2003; Operation Market Sweep, Operation Vigilant Resolve and Operation Phantom Fury in Fallujah in 2004; Operation Matador in Anbar, Operation Squeeze Play and Operation Lightning in Baghdad, Operation New Market near Haditha, Operation Spear in Karabillah and the Battle of Tal Afar – all in 2005; Operation Swarmer in Samarra and Operation Together Forward in Baghdad in 2006; and Operation Law and Order in Baghdad, Operation Arrowhead Ripper in Baqouba and Operation Phantom Strike throughout Iraq – all in 2007.

• Challenge Project
• Iraqi civil war (2006–2008)
• Iraqi insurgency (2011–2013)
• Consolation payment
• Fallujah during the Iraq War
• Juba (sniper)
• List of revolutions and rebellions
• Iraq War order of battle, 2009
• USA kill or capture strategy in Iraq
• USA list of most-wanted Iraqis
• Taliban insurgency
• Joint Special Operations Command Task Force in the Iraq War
• Task Force ODIN
• Executive Order 13303

Chronology:

• History of Iraq (2003–11)
  • 2003 in Iraq
  • 2004 in Iraq
  • 2005 in Iraq
  • 2006 in Iraq
  • 2007 in Iraq
  • 2008 in Iraq
    • 2008 Mosul offensive
  • 2009 in Iraq
  • 2010 in Iraq
  • 2011 in Iraq

• Bishku, Michael B. (2018), Israel and the Kurds: A Pragmatic Relationship in Middle Eastern Politics, vol. 41, Journal of South Asian and Middle Eastern Studies

• Chehab, Zaki. Iraq Ablaze: Inside the Insurgency, I. B. Tauris & Co Ltd. ISBN 1-84511-110-9.
• Who Are the Insurgents? Sunni Arab Rebels in Iraq U.S. Institute of Peace Special Report, April 2005
• Rogers, Paul. Iraq and the War on Terror: Twelve Months of Insurgency. I.B. Tauris. ISBN 1-84511-205-9.
• Hashim, Ahmed S. Insurgency and Counter-Insurgency in Iraq. I.B. Tauris. ISBN 0-8014-4452-7. JSTOR
• Enders, David. Baghdad Bulletin: Dispatches on the American Occupation University of Michigan Press (4 April 2005) ISBN 0-472-11469-7 JSTOR
• O'Connell, Edward. Bruce R. Pirnie. Counterinsurgency in Iraq: 2003–2006/ RAND ISBN 978-0-8330-4297-2.
• Jürgen Todenhöfer Why do you kill? The untold story of the Iraqi resistance.