George Bush, speaking in October 2002, said that “The stated policy of the United States is regime change… However, if Hussein were to meet all the conditions of the United Nations, the conditions that I have described very clearly in terms that everybody can understand, that in itself will signal the regime has changed”. Based on claims from certain intelligence sources, Bush stated on March 6, 2003 that he believed that Hussein was not complying with UN Resolution 1441.

In September 2002, Tony Blair stated, in an answer to a parliamentary question, that “Regime change in Iraq would be a wonderful thing. That is not the purpose of our action; our purpose is to disarm Iraq of weapons of mass destruction” In November of that year, Blair further stated that, “So far as our objective, it is disarmament, not régime change - that is our objective. Now I happen to believe the regime of Saddam is a very brutal and repressive regime, I think it does enormous damage to the Iraqi people... so I have got no doubt Saddam is very bad for Iraq, but on the other hand I have got no doubt either that the purpose of our challenge from the United Nations is disarmament of weapons of mass destruction, it is not regime change.”

At a press conference on January 31, 2003, Bush again reiterated that the single trigger for the invasion would be Iraq’s failure to disarm, “Saddam Hussein must understand that if he does not disarm, for the sake of peace, we, along with others, will go disarm Saddam Hussein.” As late as February 25, 2003, it was still the official line that the only cause of invasion would be a failure to disarm. As Blair made clear in a statement to the House of Commons, “I detest his regime. But even now he can save it by complying with the UN's demand. Even now, we are prepared to go the extra step to achieve disarmament peacefully.”

Additional justifications used at various times included Iraqi violation of UN resolutions, the Iraqi government's repression of its citizens, and Iraqi violations of the 1991 cease-fire.

The main allegations were that Hussein possessed or was attempting to produce weapons of mass destruction which Saddam Hussein, had used such as in Halabja, possessed, and made efforts to acquire. Particularly considering two previous attacks on Baghdad nuclear weapons production facilities by both Iran and Israel which was alleged to have postponed weapons development progress. And that he had ties to terrorists, specifically al-Qaeda.

While it never made an explicit connection between Iraq and the September 11 attacks, the George W. Bush administration repeatedly insinuated a link, thereby creating a false impression for the US public. Grand jury testimony from the 1993 World Trade Center attack trials cited numerous direct linkages from the bombers to Baghdad and Department 13 of the Iraqi Intelligence Service in that initial attack marking the second anniversary to vindicate the surrender of Iraqi armed forces in Operation Desert Storm. For example, The Washington Post has noted that,

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While not explicitly declaring Iraqi culpability in the September 11, 2001, terrorist attacks, administration officials did, at various times, imply a link. In late 2001, Cheney said it was "pretty well confirmed" that attack mastermind Mohamed Atta had met with a senior Iraqi intelligence official. Later, Cheney called Iraq the "geographic base of the terrorists who had us under assault now for many years, but most especially on 9/11."

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Steven Kull, director of the Program on International Policy Attitudes (PIPA) at the University of Maryland, observed in March 2003 that "The administration has succeeded in creating a sense that there is some connection [between Sept. 11 and Saddam Hussein]". This was following a New York Times/CBS poll that showed 45% of Americans believing Saddam Hussein was "personally involved" in the September 11 atrocities. As the Christian Science Monitor observed at the time, while "Sources knowledgeable about US intelligence say there is no evidence that Hussein played a role in the Sept. 11 attacks, nor that he has been or is currently aiding Al Qaeda... the White House appears to be encouraging this false impression, as it seeks to maintain American support for a possible war against Iraq and demonstrate seriousness of purpose to Hussein's regime." The CSM went on to report that, while polling data collected "right after Sept. 11, 2001" showed that only 3 percent mentioned Iraq or Saddam Hussein, by January 2003 attitudes "had been transformed" with a Knight Ridder poll showing that 44% of Americans believed "most" or "some" of the September 11 hijackers were Iraqi citizens.

The BBC has also noted that while President Bush, "never directly accused the former Iraqi leader of having a hand in the attacks on New York and Washington", he, "repeatedly associated the two in keynote addresses delivered since September 11", adding that, "Senior members of his administration have similarly conflated the two." For instance, the BBC report quotes Colin Powell in February 2003, stating that, "We've learned that Iraq has trained al-Qaeda members in bomb-making and poisons and deadly gases. And we know that after September 11, Saddam Hussein's regime gleefully celebrated the terrorist attacks on America." The same BBC report also noted the results of a recent opinion poll, which suggested that "70% of Americans believe the Iraqi leader was personally involved in the attacks."

Also in September 2003, the Boston Globe reported that "Vice President Dick Cheney, anxious to defend the White House foreign policy amid ongoing violence in Iraq, stunned intelligence analysts and even members of his own administration this week by failing to dismiss a widely discredited claim: that Saddam Hussein might have played a role in the Sept. 11 attacks." A year later, presidential candidate John Kerry alleged that Cheney was continuing "to intentionally mislead the American public by drawing a link between Saddam Hussein and 9/11 in an attempt to make the invasion of Iraq part of the global war on terror."

Throughout 2002, the Bush administration insisted that removing Hussein from power to restore international peace and security was a major goal. The principal stated justifications for this policy of "regime change" were that Iraq's continuing production of weapons of mass destruction and known ties to terrorist organizations, as well as Iraq's continued violations of UN Security Council resolutions, amounted to a threat to the US and the world community.

The Bush administration's overall rationale for the invasion of Iraq was presented in detail by US Secretary of State Colin Powell to the United Nations Security Council on February 5, 2003. In summary, he stated,

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We know that Saddam Hussein is determined to keep his weapons of mass destruction; he's determined to make more. Given Saddam Hussein's history of aggression... given what we know of his terrorist associations and given his determination to exact revenge on those who oppose him, should we take the risk that he will not some day use these weapons at a time and the place and in the manner of his choosing at a time when the world is in a much weaker position to respond? The United States will not and cannot run that risk to the American people. Leaving Saddam Hussein in possession of weapons of mass destruction for a few more months or years is not an option, not in a post-September 11 world.

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Since the invasion, the US and British government claims concerning Iraqi weapons programs and links to terrorist organizations have been discredited. While the debate of whether Iraq intended to develop chemical, biological, and nuclear weapons in the future remains open, no WMDs have been found in Iraq since the invasion despite comprehensive inspections lasting more than 18 months. In Cairo, on February 24, 2001, Colin Powell had predicted as much, saying, "Hussein has not developed any significant capability with respect to weapons of mass destruction. He is unable to project conventional power against his neighbours." Similarly, assertions of significant operational links between the Iraqi regime and al Qaeda have largely been discredited by the intelligence community, and Secretary Powell himself eventually admitted he had no incontrovertible proof.

In September 2002, the Bush administration said attempts by Iraq to acquire thousands of high-strength aluminium tubes pointed to a clandestine program to make enriched uranium for nuclear bombs. Powell, in his address to the UN Security Council just before the war, referred to the aluminium tubes. A report released by the Institute for Science and International Security in 2002, however, reported that it was highly unlikely that the tubes could be used to enrich uranium. Powell later admitted he had presented an inaccurate case to the United Nations on Iraqi weapons, based on sourcing that was wrong and in some cases "deliberately misleading."

The Bush administration asserted that the Hussein government had sought to purchase yellowcake uranium from Niger. On March 7, 2003, the US submitted intelligence documents as evidence to the International Atomic Energy Agency. These documents were dismissed by the IAEA as forgeries, with the concurrence in that judgment of outside experts. At the time, a US official claimed that the evidence was submitted to the IAEA without knowledge of its provenance and characterized any mistakes as "more likely due to incompetence not malice".

Unmanned Iraqi drones

In October 2002, a few days before the US Senate vote on the Authorization for Use of Military Force Against Iraq Resolution, about 75 senators were told in closed session that the Iraqi government had the means of delivering biological and chemical weapons of mass destruction by unmanned aerial vehicle (UAV) drones that could be launched from ships off the US' Atlantic coast to attack US eastern seaboard cities. Colin Powell suggested in his presentation to the United Nations that UAVs were transported out of Iraq and could be launched against the US. In fact, Iraq had no offensive UAV fleet or any capability of putting UAVs on ships. Iraq's UAV fleet consisted of less than a handful of outdated Czech training drones. At the time, there was a vigorous dispute within the intelligence community whether the CIA's conclusions about Iraq's UAV fleet were accurate. The US Air Force agency denied outright that Iraq possessed any offensive UAV capability.

Human rights

As evidence supporting U.S. and British claims about Iraqi WMDs and links to terrorism weakened, some claim supporters of the invasion have increasingly shifted their justification to the human rights violations of the Hussein government. Leading human rights groups such as Human Rights Watch have argued, however, that they believe human rights concerns were never a central justification for the invasion, nor do they believe that military intervention was justifiable on humanitarian grounds, most significantly because "the killing in Iraq at the time was not of the exceptional nature that would justify such intervention." Many supporters of the war, however, claim from the start human rights concerns were among the reasons given for the invasion, and that the threat of weapons of mass destruction was emphasized at the United Nations, since this dealt with Iraq flouting UN resolutions. They further claim human rights groups that oppose the war have no objective standard regarding when to invade a country.