The 2003 invasion of Iraq was the first stage of the Iraq War. The invasion began on 20 March 2003 and lasted just over one month, including 26 days of major combat operations. The invasion was conducted by a United States–led coalition of mainly American, British, Australian, and Polish troops.
According to US president George W. Bush and UK prime minister Tony Blair, the coalition aimed to disarm Iraq of weapons of mass destruction (WMDs)—nuclear, chemical, and biological weapons—and "free the Iraqi people" by deposing president Saddam Hussein, in turn ending his "support for terrorism". Before the invasion, United Nations (UN) inspectors in Iraq had found no evidence of Iraqi WMDs; US and British officials claimed they were still hidden, and posed an immediate threat to world peace.
The invasion was strongly opposed by some long-standing US allies, including Canada, France, Germany, and New Zealand. In 2004, UN secretary-general Kofi Annan called the invasion illegal under international law, as a breach of the UN Charter. On 15 February 2003, there were worldwide protests against the anticipated invasion of Iraq, including a rally of three million people in Rome which was the largest anti-war rally in history.
The invasion began with an airstrike on the Presidential Palace in Baghdad on 20 March 2003. The following day, coalition forces launched an incursion into Basra Governorate from their massing point close to the Iraqi–Kuwaiti border. While special forces launched an amphibious assault from the Persian Gulf to secure Basra and the surrounding petroleum fields, the main invasion army occupied southern Iraq, 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 were met with little resistance. Most of the Iraqi military was quickly defeated. On 9 April 2003, 22 days after the first day of the invasion, the capital city of Baghdad was captured by coalition forces after the six-day-long Battle of Baghdad. Other operations included the capture and occupation of Kirkuk on 10 April and the attack on and capture of Tikrit on 15 April. Saddam and the Iraqi central leadership went into hiding, as the coalition forces finished occupying the country. On 1 May, Bush declared the "end of major combat operations" in Iraq; this began the occupation phase of the Iraq War, in which coalition forces fought the Iraqi insurgency. Saddam was captured by US forces on 13 December 2003.
The Gulf War began in 1990, and ended in 1991 with a ceasefire between the United Nations coalition and Iraq. The U.S. and its allies tried to keep Saddam Hussein in check with military actions such as Operation Southern Watch, by monitoring and controlling some Iraqi airspace, as well as using economic sanctions. Violating the Biological Weapons Convention, Iraq's biological weapons (BW) program began in the early 1980s, with help from the U.S. and European countries reportedly unaware of Iraq's intentions. Details of Iraqi biological and chemical weapons program surfaced after the Gulf War, following investigations by the UN Special Commission (UNSCOM), which had been charged with the post-war disarmament of Iraq. The investigation concluded that the program had not continued after the war. The U.S. and its allies then maintained a policy of "containment" towards Iraq, involving numerous economic sanctions by the UN Security Council (UNSC); the enforcement of Iraqi no-fly zones declared by the U.S. and the UK to protect the Kurds in Iraqi Kurdistan and Shias in the south from aerial attacks by the Iraqi government; and ongoing inspections. Iraqi military helicopters and planes regularly contested the no-fly zones.
In 1998, regime change in Iraq became official U.S. foreign policy with enactment of the Iraq Liberation Act, enacted following the expulsion of UN weapons inspectors months earlier (some had been accused of spying for the U.S.). The act provided $97 million for Iraqi "democratic opposition organizations" to "establish a program to support a transition to democracy in Iraq." This legislation contrasted with the terms set out in UNSC Resolution 687, which focused on weapons and weapons programs and made no mention of regime change. One month later, the U.S. and UK bombed Iraq during Operation Desert Fox, their rationale being to hamper Iraq's ability to produce chemical, biological, and nuclear weapons, but U.S. intelligence personnel also hoped it would help weaken Saddam's grip on power.
With George W. Bush's inauguration in January 2001, the U.S. moved towards a more aggressive policy toward Iraq. The Republican Party's 2000 campaign platform called for the U.S. to "remove" Saddam. After leaving the Bush administration, Treasury Secretary Paul O'Neill said that an attack on Iraq had been planned since Bush's inauguration, and that the first U.S. National Security Council meeting involved discussion of an invasion. O'Neill later backtracked, saying that these discussions were part of a continuation of foreign policy first put into place by the Clinton administration. Despite the Bush administration's stated interest in invading Iraq, little formal movement towards an invasion occurred until the 11 September attacks (9/11).
On the morning of 11 September 2001, the al-Qaeda militant organization, led by Osama bin Laden, committed four coordinated terrorist attacks on the U.S., using hijacked commercial airliners to crash into major symbols of American economic and military power. Nearly 3,000 people were killed. Messages intercepted by the National Security Agency during the attacks pointed to al-Qaeda's responsibility for them. By mid-afternoon, however, Secretary of Defense Donald Rumsfeld ordered the Pentagon to prepare plans for attacking Iraq. According to aides near him that day, Rumsfeld messaged: "Best info fast. Judge whether good enough hit S.H. [Saddam Hussein] at same time. Not only UBL [Usama bin Laden]". According to the 9/11 Commission Report, "Rumsfeld later explained that at the time, he had been considering either one of them, or perhaps someone else, as the responsible party."
On 12 September, Bush ordered White House counter-terrorism coordinator Richard A. Clarke to investigate possible Iraqi involvement in 9/11. Shocked by the sophistication of the attacks, the administration wondered whether a state sponsor was involved. Clarke's office issued a memo on 18 September that noted wide ideological gaps between Iraq and al-Qaeda, and that only weak anecdotal evidence linked the two. A 21 September briefing to Bush indicated that U.S. intelligence had no evidence linking Saddam to the attacks, and there was "scant credible evidence that Iraq had any significant collaborative ties with al-Qaeda." The PDB wrote off the few contacts that existed between Saddam's government and al-Qaeda as attempts to monitor the group, not work with it.
However, U.S. vice president Dick Cheney and Rumsfeld expressed skepticism toward's the CIA's intelligence. They questioned whether the CIA were competent enough to produce accurate information as the agency underestimated threats and failed to accurately predict events such as the 1979 Iranian Revolution, the 1990 Iraqi invasion of Kuwait, and the 1991 collapse of the Soviet Union. They instead preferred outside analysis, of which information was supplied by the Iraqi National Congress as well as unvetted pieces of intelligence. This information alleged that a highly secretive relationship existed between Saddam and al-Qaeda from 1992, specifically through a series of meetings reportedly involving the Iraqi Intelligence Service (IIS). The rationale for invading Iraq as a response to 9/11 has been widely questioned, as there was no cooperation between Saddam and al-Qaeda.