The Iraq war was mounted on flawed intelligence, was executed with "wholly inadequate" planning, and ended "a long way from success," according to a damning report released Wednesday by the head of Britain's Iraq War inquiry.
Retired civil servant John Chilcot, who oversaw the seven-year inquiry, said "the U.K. chose to join the invasion of Iraq before the peaceful options for disarmament had been exhausted. Military action at that time was not a last resort."
The 2.6-million-word report is an exhaustive verdict on a divisive conflict that — by the time British combat forces left in 2009 — had killed 179 British troops, almost 4,500 American personnel and more than 100,000 Iraqis.
It continues to divide Britain and overshadows the legacy of then-Prime Minister Tony Blair. As Chilcot introduced his report at a London conference center on Wednesday, dozens of anti-war protesters with placards reading "Bliar" rallied outside.
Chilcot said Blair's government presented an assessment of the threat posed by Saddam Hussein's weapons with "certainty that was not justified." He also found military planning for the war and its aftermath were not up to the task.
"The people of Iraq have suffered greatly" because of a military intervention "which went badly wrong," he said.
In a statement, Blair said he would "take full responsibility for any mistakes without exception or excuse."
But he said he made the decision to go to war "in good faith and in what I believed to be the best interests of the country."
Anti-war activists and relatives of some dead British troops had hoped the report would find the conflict illegal, opening the way for Blair to be prosecuted for war crimes.
Chilcot refrained from saying whether the 2003 invasion was legal and didn't accuse Blair of deliberately misleading the public or Parliament. But he said that "the circumstances in which it was decided that there was a legal basis for U.K. military action were far from satisfactory."
Relatives of soldiers killed in the conflict said they hadn't ruled out legal action.
"All options are open," said Matthew Jury, a lawyer for some of the families.
In a statement, a group of families said "we must use this report to make sure all parts of the Iraq fiasco are never repeated again."
"Never again must so many mistakes be allowed to sacrifice British lives and lead to the destruction of a country for no positive end," they said.
Chilcot heard from 150 witnesses and analyzed 150,000 documents. His conclusions are a blow to Blair, who told President George W. Bush eight months before the March 2003 invasion — without consulting government colleagues — "I will be with you whatever."
The report says Blair went to war to stand shoulder-to-shoulder with Britain's main ally, only to find the U.K. excluded from most important decision-making about the military campaign and its aftermath.
"Mr. Blair, who recognized the significance of the post-conflict phase, did not press President Bush for definite assurances about U.S. plans," the report concluded.
Iraq descended into sectarian strife after the occupiers dismantled Saddam 's government and military apparatus, unleashing chaos that helped give rise to the Islamic State group.
The report found failings by military chiefs who did not provide adequate equipment to forces in the field, and whose main post-invasion strategy "was to reduce the level of (U.K.) deployed forces."
The report concludes that Britain's combat mission, which ended in 2009, did not achieve the objectives laid out in 2003 and saw British forces make a "humiliating" deal with militias in southern Iraq to avoid attacks.
"The U.K. failed to plan or prepare for the major reconstruction program required in Iraq," the report said.
The war has overshadowed the legacy of Blair, whose government has been accused of exaggerating intelligence about Saddam's alleged weapons of mass destruction in order to build support for the invasion.
Chilcot criticized spy chiefs who failed to ensure their partial intelligence about Saddam's weapons was not hardened into certainty by government spin. He said they also failed to consider "that Iraq might no longer have chemical biological or nuclear weapons" — which turned out to be the case.
The report said the widespread perception that the government had exaggerated intelligence evidence "has produced a damaging legacy, including undermining trust and confidence in government statements."
Long-term, that perception will "make it very much more difficult for any prime minister to be able to take Britain into a foreign conflict on the same basis again," George Joffe, a Middle East expert and visiting professor at King's College London, told The Christian Science Monitor earlier this week.
Blair — who declined to comment on the report before publication — has always said his government did not invent or distort intelligence.
The report also faults him for making key decisions with only a few key aides rather than through collective Cabinet consultation.
Chilcot's report has been repeatedly delayed, in part by wrangling over the inclusion of classified material, including conversations between Blair and Bush. Some of Blair's pre-war letters to the president are published in Chilcot's report, but not Bush's replies.
It remains unclear what, if any, legal action could be taken against Blair or others.
The International Criminal Court is looking into alleged war crimes by British troops in Iraq, but says has said that Britain's decision to go to war falls outside its jurisdiction.
Sarah O'Connor, whose airman brother died in a plane crash in Iraq in 2005, said the war remained "an indelible stain on the whole world."
"There is one terrorist in the world that the world needs to be aware of, and his name is Tony Blair," she said.
Associated Press writer Danica Kirka contributed to this story.