Thirteen years after British troops marched into Iraq and seven years after they left a country that's still mired in violence, John Chilcot's long-delayed, 2.6 million-word report on the divisive war and its chaotic aftermath addresses the lingering question: What went wrong?

Chilcot's inquiry held public hearings between 2009 and 2011, taking evidence from more than 150 witnesses — including former British prime minister Tony Blair. The inquiry analysed 150,000 documents and cost more than 10 million pounds ($13 million), but its report has been repeatedly delayed, in part by wrangling over the inclusion of classified material — including conversations between Blair and former US president George Bush.

Opponents of the war claim Blair's government exaggerated evidence that Iraqi dictator Saddam Hussein had weapons of mass destruction that threatened the West — the foundation of the case for war. No chemical, biological or nuclear weapons were found in Iraq. Previous inquiries, limited in scope, had largely absolved the government of blame.

In this picture gallery, IBTimes UK looks back at Britain's involvement in the Iraq war between 2003 and 2009.

Iraq war
179 British military personnel lost their lives during the Iraq war MoD

The US-led conflict killed 179 British troops and some 4,500 American military personnel. It also helped trigger violence that killed hundreds of thousands of Iraqis and still rocks the Middle East. Iraq descended into sectarian strife after the occupiers dismantled Saddam Hussein's government and military apparatus, unleashing chaos that helped give rise to the Sunni extremist militants of the Islamic State group.