A coalition of US and British troops invaded Iraq on March 20, 2003.
They fought to overthrow then President Saddam Hussein from a move based largely on a claim that he possessed weapons of mass destruction.
Those weapons were never found.
The war that followed is estimated to have killed hundreds of thousands of Iraqis, unleashed 13 years of sectarian violence and destroyed Iraq's institutions and infrastructure.
For the past seven years, a British inquiry has investigated the events that led to the invasion, and what lessons should be learnt.
The chairman of the inquiry, Sir John Chilcot, has delivered a damning indictment of British policy.
He says claims made about the threat posed by Iraq’s weapons of mass destruction were not substantiated.
And they were presented with a certainty that was unjustified.
Despite explicit warnings, Chilcot says the consequences of the invasion were underestimated by the government.
And that planning and preparation for a post-invastion Iraq were, in his words, "wholly inadequate".
Chilcot also questioned the legal basis for going to war, saying it was "far from satisfactory".
So, could the blunder happen again?
Presenter: Martine Dennis
Nafeez Ahmed, Middle East Eye columnist.
Piers Robinson, Senior Lecturer in International Politics at the University of Manchester.
Frank Ledwidge, Senior Fellow at the Royal Air Force College at the University of Portsmouth.
Source: Al Jazeera