The world was divided in 2003 into countries that supported or opposed the Iraq war. The UN was in the middle. Here we recount the arguments for and against made by eight key players, and where they stand now.
The battle over Iraq in the UN Security Council raised doubts about the organisation's role in the 21st Century. Secretary General Kofi Annan vainly appealed for compromise and unity. But as France, China and Russia threatened to veto a US-backed resolution authorising force against Iraq, he realised the die was cast. The UN began instead to prepare for the humanitarian consequences of war.
In the first few months of the conflict the UN's headquarters in Baghdad was bombed, killing its most senior official. Mr Annan called the attack "the darkest day in our lives".
In September 2004, he said for the first time that the decision to go to war without a second resolution was illegal. "I have indicated it was not in conformity with the UN charter from our point of view - from the charter point of view - it was illegal," he told the BBC. In his final speech as UN head, in late 2006, he again attacked US unilateralism, saying: "No nation can make itself secure by seeking supremacy over others."
JOSE MARIA AZNAR
Spanish Prime Minister Jose Maria Aznar's support for the Iraq war marked a realignment in Europe's relations with the US. A member of the UN Security Council as the preparations for war advanced, Mr Aznar stood shoulder to shoulder with the US and the UK, rather than France and Germany.
"There is nothing more dangerous than a political leader who builds castles in the air, and I believe political leaders who raise false hopes, who don't look at the world as it is, are set to reap failure," Mr Aznar said after a meeting with Mr Bush in February 2003. The next month he took part in a key pre-war summit with Mr Bush and Mr Blair in the Azores. Huge protests occurred in August, as Spanish troops departed for Iraq.
In 2007, Mr Aznar - whose party was beaten in the 2004 elections - acknowledged that he had over-estimated the threat posed by Saddam Hussein: "The whole world thought Iraq had weapons of mass destruction and they didn't, I know that now. When I didn't know, no-one knew."
Former British Prime Minister Tony Blair's backing for war - as the only way of ridding Iraq of weapons of mass destruction - came to define his premiership. In a speech before parliament on March 18 2003, he argued that Saddam Hussein's "diplomatic dance" meant that threats were only effective if backed with force: "The only persuasive power to which he responds is 250,000 allied troops on his doorstep."
His decision to go to war was backed in parliament but brought the biggest parliamentary rebellion ever recorded against a British government, and prompted three ministers to resign.
He has recognised that the intelligence on his decision was based was flawed but has not apologised. In 2006, he admitted he had struggled with his conscience over the decision to go to war, saying he would be judged by history and God. A year later he told The Times: "If there's anything I regret... it is... not having laid out for people in a clearer way what I saw as the profound nature of this struggle and the fact that it was going to go on for a generation."
Plucked from retirement to lead the team of UN weapons inspectors sent in to Iraq, the pragmatic and calm Hans Blix asked in vain for more time to continue checking for Iraqi weapons of mass destruction (WMD).
His anger about the military intervention spilled over just months after the bombing began. In a series of scathing attacks on the UK and the US, he accused them of organising the war well before the outcome of his work was known and dramatising the threat of WMD to support their campaign. "There is evidence that this war was planned well in advance. Sometimes this raises doubts about their attitude to the [weapons] inspections," he told the Spain's El Pais in April 2003.
A year later, he compared the US attitude to the hunt for WMD to a "witch-hunt", saying the US had made "monumental" and "scandalous" errors of intelligence. His opinions have not changed. In 2007 he said: "I think everything in Iraq after the invasion has been a tragedy. The only positive thing I think is the disappearance of Saddam Hussein."
GEORGE W BUSH
The US president said he had three reasons for going to war against Iraq - to disarm the country of its WMD, to end Saddam Hussein's support for terrorism and to free the Iraqi people. "The attacks of September 11 2001, show what the enemies of America did with four airplanes. We will not wait to see what terrorists or terrorist states could do with weapons of mass destruction," he said in March 2003.
Two months into a war that his Defence Secretary, Donald Rumsfeld, said would probably last no longer than six, Mr Bush announced that major combat operations in Iraq were over. "The tyrant has fallen, and Iraq is free," Mr Bush said from an aircraft carrier off the Californian coast.
Three years later, he seemed willing to concede that the situation in Iraq could be compared to Vietnam but continued to describe it as the latest battlefield in the war on terror. In January 2007, he announced that an additional 20,000 US troops would be sent to Iraq to bolster the lawless regions around the capital.
Despite his administration's acknowledgement of intelligence failures, Mr Bush has remained steadfast in his defence of his decision to go to war, saying in March 2008: "The decision to remove Saddam Hussein was the right decision early in my presidency; it is the right decision at this point in my presidency; and it will forever be the right decision."
Russia's ambassador to the United Nations was one of the key mouthpieces for his country's opposition to the US-led proposal to intervene militarily. "Russia never considered war as an adequate tool to resolve the Iraqi issue," he said. Russia, along with France, opposed the idea of a second UN resolution to authorise the use of force. In an address just a few days after the conflict began, he called the military action "unprovoked" and said it violated international law and the UN charter.
Russia's anger over the war contributed to a deepening diplomatic rift between the two countries, prompting talk of a new Cold War. Critics claim Russia's opposition to the Iraq war was due to its oil interests in the country.
Five years on, as Russia's Foreign Minister, Mr Lavrov continues to argue that the conflict threatens to destabilise Iraq's immediate neighbours and the region as a whole. He has repeatedly called on the international community to withdraw foreign troops and says strengthened Iraqi forces should be given responsibility for security.
Former US Secretary of State Colin Powell presented the detailed and controversial evidence for going to war against Iraq to the UN in February 2003. He referred to spy satellite photos and intercepted conversations between Iraqi officials as he asserted that Saddam Hussein's regime was hiding WMD: "Numerous human sources tell us that the Iraqis are moving, not just documents and hard drives, but weapons of mass destruction to keep them from being found by inspectors."
It was a speech that would come to haunt him. A year later he conceded that some of the information - on the country's development of mobile labs for making biological weapons - "appears not to be... that solid". In September 2005, more than a year after he resigned as head of the State Department, he described the speech as a "blot" on his record. "It will always be a part of my record. It was painful. It's painful now," he said.
In 2007, he revealed that he had tried to dissuade George W Bush from intervening militarily in Iraq, a country which he now said was a state of civil war. "I tried to avoid this war. I took him through the consequences of going into an Arab country and becoming the occupiers."
DOMINIQUE DE VILLEPIN
Former French Foreign Minister Dominique de Villepin led his country's opposition to the war in Iraq, successfully blocking a second UN resolution proposed by the US and UK authorising the use of force. In a much-quoted speech to the UN Security Council on 14 February 2003, Mr de Villepin eloquently defended the diplomatic process: "The option of war might seem a priori to be the swiftest. But let us not forget that having won the war, one has to build peace," he said.
France threatened to employ its Security Council veto against a second UN resolution authorising the use of force. This, combined with France's rejection of a series of disarmament tests proposed by the UK, led to accusations that he was poisoning the very same process he wanted to protect. In response, Mr de Villepin said: "It isn't a matter of according a few more days to Iraq before resorting to force, but to resolutely advance on the path of peaceful disarmament created by the inspections, which are a credible alternative to war."
His prominent anti-Iraq role, brought huge popularity in France, and helped catapult him into the job of France's prime minister, which he held between 2005 and 2007.