The 2003 invasion of Iraq lasted from 19 March 2003 to 1 May 2003

The 2003 invasion of Iraq lasted from 19 March 2003 to 1 May 2003, and signaled the start of the conflict that later came to be known as the Iraq War, which was dubbed Operation Iraqi Freedom by the United States. The invasion consisted of 21 days of major combat operations, in which a combined force of troops from the United States, the United Kingdom, Australia, and Poland, invaded Iraq and deposed the Ba'athist government of Saddam Hussein. The invasion phase consisted primarily of a conventionally-fought war which concluded with the capture of the Iraqi capital of Baghdad by American forces.

Four countries participated with troops during the initial invasion phase, which lasted from 19 March to 9 April 2003. These were the United States (148,000), United Kingdom (45,000), Australia (2,000), and Poland (194). 36 other countries were involved in its aftermath. In preparation for the invasion, 100,000 U.S. troops were assembled in Kuwait by 18 February.[20] The United States supplied the majority of the invading forces, but also received support from Kurdish irregulars in Iraqi Kurdistan.

According to U.S. President George W. Bush and British Prime Minister Tony Blair, the coalition mission was "to disarm Iraq of weapons of mass destruction, to end Saddam Hussein's support for terrorism, and to free the Iraqi people."[21] Former chief counter-terrorism adviser on the National Security Council Richard A. Clarke believes Bush took office with a predetermined plan to invade Iraq.[22] Others place a much greater emphasis on the impact of the 11 September 2001 attacks, and the role this played in changing U.S. strategic calculations, and the rise of the freedom agenda.[23] According to Blair, the trigger was Iraq's failure to take a "final opportunity" to disarm itself of alleged nuclear, chemical, and biological weapons that U.S. and British officials called an immediate and intolerable threat to world peace.[24] In 2005, the Central Intelligence Agency released a report saying that no weapons of mass destruction had been found in Iraq.[25]

In a January 2003 CBS poll 64% of Americans had approved of military action against Iraq, however 63% wanted Bush to find a diplomatic solution rather than go to war, and 62% believed the threat of terrorism directed against the U.S. would increase due to war.[26] The invasion of Iraq was strongly opposed by some long-standing U.S. allies, including the governments of France, Germany, New Zealand, and Canada.[27][28][29] Their leaders argued that there was no evidence of weapons of mass destruction in Iraq and that invading the country was not justified in the context of UNMOVIC's 12 February 2003 report. On 15 February 2003, a month before the invasion, there were worldwide protests against the Iraq War, including a rally of three million people in Rome, which is listed in the Guinness Book of Records as the largest ever anti-war rally.[30] According to the French academic Dominique Reynié, between 3 January and 12 April 2003, 36 million people across the globe took part in almost 3,000 protests against the Iraq war.[31]

The invasion was preceded by an air strike on the Presidential Palace in Baghdad on 19 March 2003. The following day coalition forces launched an incursion into Basra Province from their massing point close to the Iraqi-Kuwaiti 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. Iraqi President Saddam Hussein 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 period and beginning the military occupation period.

As of December 2011, the 2003 invasion of Iraq was the most recent armed conflict between standing national armies causing at least 1,000 battle deaths.