US and UK leaders floated many reasons for the war on Iraq before it began. But Iraq's alleged possession of weapons of mass destruction - in defiance of United Nations resolutions - was among the most frequently mentioned.
Here is a selection of reasons for action articulated in the run-up to the war.
George W Bush speaking to the UN, 13 September 2002:
To suspend hostilities [in 1991], to spare himself, Iraq's dictator accepted a series of commitments. The terms were clear to him and to all, and he agreed to prove he is complying with every one of those obligations...
He has proven instead only his contempt for the United Nations and for all his pledges. By breaking every pledge, by his deceptions and by his cruelties, Saddam Hussein has made the case against himself.
United Nations Resolution 1441, 8 November:
Iraq has been and remains in material breach of its obligations under relevant resolutions... in particular through Iraq's failure to co-operate with United Nations weapons inspectors and the IAEA [International Atomic Energy Agency].
Mr Bush's State of the Union address, 29 January 2003:
Today, the gravest danger in the war on terror, the gravest danger facing America and the world, is outlaw regimes that seek and possess nuclear, chemical, and biological weapons. These regimes could use such weapons for blackmail, terror, and mass murder...
Twelve years ago, Saddam Hussein faced the prospect of being the last casualty in a war he had started and lost. To spare himself, he agreed to disarm of all weapons of mass destruction.
For the next 12 years, he systematically violated that agreement. He pursued chemical, biological and nuclear weapons even while inspectors were in his country...
The dictator of Iraq is not disarming. To the contrary, he is deceiving.
Colin Powell briefing to the UN Security Council, 6 February:
The burden is on Iraq to comply and disarm. Inspectors are inspectors, not detectives.... Saddam Hussein and his regime are doing everything they can to make sure the inspectors find absolutely nothing...
We must not shrink from whatever is ahead of us. We must not fail in our duty and our responsibilities. Clearly, Saddam will stop at nothing until something stops him.
UK Prime Minister Tony Blair, speaking on the BBC's Iraq: Britain Decides programme, 12 February:
Before we take the decision to go to war, the morality of that should weigh heavily on our conscience because innocent people, as well as the guilty, die in a war.
But the alternative is to carry on with a sanctions regime which, because of the way Saddam Hussein implements it, leads to thousands of people dying needlessly in Iraq every year.
US Defence Secretary Donald Rumsfeld, speaking to the press, 12 March:
The credibility of the UN is important to the world... The question before the United Nations is clear: Is Saddam Hussein taking this final opportunity that was offered by Resolution 1441 to disarm or not?
And the answer to the question, it strikes me, is increasingly obvious. He makes a show of destroying a handful of missiles; missiles which he claimed in his declaration did not violate UN restrictions, but now admits that they do violate UN restrictions.
He claims to have no chemical or biological weapons, yet we know he continues to hide biological and chemical weapons, moving them to different locations as often as every 12 to 24 hours, and placing them in residential neighbourhoods.
Australian Prime Minister John Howard, in a nationally televised address from parliament, 13 March:
I have the strongest possible belief that the world must confront the twin evils of the spread of weapons of mass destruction to rogue states and the danger of those weapons falling into the hands of international terrorists.
Azores statement by Mr Bush, Mr Blair and Spanish Prime Minister Jose Maria Aznar, 16 March:
Iraq's talented people, rich culture and tremendous potential have been hijacked by Saddam Hussein.
His brutal regime has reduced a country with a long and proud history to an international pariah that oppresses its citizens, started two wars of aggression against its neighbours, and still possesses a grave threat to the security of its region and the world.
Saddam's defiance of United Nations Security Council resolutions demanding the disarmament of his nuclear, chemical, biological, and long-range missile capacity has led to sanctions on Iraq and has undermined the authority of the UN.
Mr Blair, speaking to the House of Commons, 18 March:
1441 is a very clear resolution. It lays down a final opportunity for Saddam to disarm. It rehearses the fact that he has been for years in material breach of 17 separate UN resolutions.
It says that this time compliance must be full, unconditional and immediate... Iraq has made some concessions to co-operation but no-one disputes it is not fully co-operating.
Iraq continues to deny that it has any WMD, though no serious intelligence service anywhere in the world believes them.
Mr Bush's ultimatum to Saddam Hussein, 18 March:
The Iraqi regime has used diplomacy as a ploy to gain time and advantage. It has uniformly defied Security Council resolutions demanding full disarmament...
The danger is clear: using chemical, biological, or, one day, nuclear weapons obtained with the help of Iraq, the terrorists could fulfil their stated ambitions and kill thousands of hundreds of thousands of innocent people in our country or any other...
Under Resolutions 678 and 687, both still in effect, the United States and our allies are authorised to use force in ridding Iraq of weapons of mass destruction...
Today, no nation can possibly claim that Iraq has disarmed. And it will not disarm so long as Saddam Hussein holds power.
Mr Rumsfeld, speaking to the Council on Foreign Relations, 27 May:
It is also possible that [the Iraqis] decided they would destroy [their weapons of mass destruction] prior to a conflict.