Explainer: Why Tony Blair has apologised for the Iraq War & the ISIS

For a long time, analysts believed that the invasion of Iraq and the rise of the terror group ISIS were linked. And the blame for the growth of the group has, time and again, been placed on the shoulders of two former world leaders - George W Bush and Tony Blair.

And then on Sunday, in an interview to CNN, former British Prime Minister Tony Blair finally acknowledged, after years of denial, that the 2003 invasion of Iraq played a part in the rise of the Islamic State. He also apologised for some mistakes in planning the war.

The interview is apparently a part of a documentary called Long Road To Hell: America In Iraq which will release this week.

The Iraq war and Blairs' decision to send troops to back the US-led invasion is still a live political issue in Britain, where a six-year public inquiry into the conflict is yet to publish its findings. Public interest in the subject even contributed to his Labour Party's loss of power in 2010.

Blair said that "there are elements of truth" in the assertion that the war caused the rise of ISIS as he took questions from CNN's Fareed Zakaria.

Blair, however, stopped short of altogether regretting the invasion, which toppled the regime and led to Saddam Hussein's execution in 2006.

"I find it hard to apologise for removing Saddam. I think even from today, in 2015, it is better that he is not there than he is there."

"Of course you can't say those of us who removed Saddam in 2003 bear no responsibility for the situation in 2015," he added, claiming that the Arab Spring had also played a role in creating instability that allowed the Islamic fundamentalist militant group to flourish.

Oddly, early this year, Blair denied he was to blame for the ISIS takeover of huge swathes of Iraq, including the country's second biggest city, Mosul.

He wrote on his website: "We have to liberate ourselves from the notion that 'we' have caused this. We haven't."

What was the basis of the Iraq War?

In October 2002, nine months before the US-led invasion of Iraq, the CIA produced a document summarising relevant intelligence on Saddam Hussein's chemical and biological weapons programmes.

The intelligence was used to support the Bush administration's case that Saddam Hussein's weapons of mass destruction (WMD) programme represented an imminent threat, which became the leading justification for the US-led war.

Earlier this year, a declassified CIA report was leaked to the press. The paper made it clear that the decision to go to war was made long before General Colin Powell had presented a litany of "evidence" of an active nuclear-weapons initiative in Iraq to the UN and Bush.

It also determined that Saddam Hussein had an active chemical weapons programme - although crucially, the CIA couldn't prove that his regime had actually produced chemical and biological agents.

There are still doubts about the existence of any such WMDs and Zakaria questioned Blair about it in the interview.

"I apologise for the fact that the intelligence we received was wrong," Blair admitted.

How did ISIS grow to be the monster it is today?

Barely three years after the US withdrawal, large parts of Iraq are now overrun by insurgents.

Spearheaded by the Islamic State of Iraq and the Levant (ISIS), Sunni rebels, including Saddam-era army officers, have seized major towns in the country.

In the process, ISIS has changed its name to the "Islamic State" and declared a caliphate that spans across parts of Iraq and Syria, with Abu-Bakr al-Baghdadi as its caliph.

The origins of ISIS lead back to Abu Musab al-Zarqawi, a Jordanian Islamist who ran terrorist training camps in Afghanistan and Pakistan, and his Jama'at al-Tawhid wal-Jihad (JTJ).

Sunni jihadis say the US prison system was their most effective organising tool

Upon entering Iraq after the US-led invasion of Afghanistan, Zarqawi built ties with Ansar al-Islam, a Kurdish Islamist group whose band of Arab fighters he led. This organisation is believed to be the "precursor" to al-Qaeda in Iraq (AQI), and not al-Qaeda itself. Later, in swearing allegiance to Osama bin Laden and his cohorts, Zarqawi's JTJ soon became known as AQI - the Iraq branch of al-Qaeda.

Following Zarqawi's death in 2006, in a US airstrike, Egyptian-born Abu Ayyub al-Masri changed the name of AQI to the Islamic State of Iraq (ISI) amid the Iraqi Civil War of 2006-07.

After violence broke out in Syria in 2011, ISI fighters traveled to that country and merged with Syrian jihadists in April 2013 to form the "Islamic State of Iraq and the Levant."

Prisoners of war and fate

A central issue for ISIS has also been the fact that Sunnis were removed from their rule, and that the West invited the rival Shia sect to take over in a predominantly Sunni nation.

The Guardian reports that "perhaps even more directly relevant to Sunni grievances and the rise of ISIS, was the US-run prison system, which started with rampant abuses at Abu Ghraib and evolved into mass detention, albeit of both major sects".

Sunni jihadis say the prison system was their most effective organising tool.

A senior ISIS commander even told the Guardian that "without the Camp Bucca facility in southern Iraq, in which he and most of the senior leadership were at one point detained, there would be no ISIS today".

"It made it all, it built our ideology," he told the Guardian last December, "We could never have all got together like this in Baghdad, or anywhere else," he said. "Here, we were not only safe, but we were only a few hundred metres away from the entire al-Qaida leadership."

The Blair-Joffe issue

At the forefront of those blaming Bush and Blair for causing such an error of massive proportions - more than 500,000 people are said to have been killed in war-related deaths sine 2003 in Iraq - is Professor George Joffe of Cambridge University.

Joffe has said time and again that Blair and Bush bear "total responsibility" for the current situation, particularly with the disastrous decision to disband the Iraqi army in May 2003 as it resulted in a power vacuum that extremists were only to happy to exploit.

Scholars have said time and again that Blair and Bush bear "total responsibility" for the situation

Speaking to The Huffington Post, Joffe said Tony Blair had a "shallow mind" and had refused to heed his warnings of post-war chaos and sectarianism in Iraq.

Which could be very true as Joffe, in 2003, was one of three Iraq experts invited into Downing Street to brief Blair on the potential fallout from an Anglo-American attack on Baghdad.

"We were not allowed to talk about whether or not it was a good idea to invade, but only about what the aftermath would be," he said, adding: "It was clear that the decision had already been made. to invade Iraq".

Blair was ridiculed publicly at the time as he had stated that he had prayed to god about whether or not he ought to send British troops to back the US invasion.

Joffe says Blair wasn't interested in the points he made. In response to warnings that the country could descend into civil war and a Sunni-led insurgency, Blair merely responded, in reference to Saddam Hussein, "But the man's evil, isn't he?"