In comments likely to anger his detractors at home and abroad who believe his decisions to intervene militarily in Iraq and Afghanistan made things worse, Blair told British TV that the Iraq crisis would have happened regardless of his actions.
"You can carry on debating about whether it was right or wrong what we did in 2003 but whatever had been done, you were always going to have a problem of deep instability in the region and in Iraq," Blair told Sky News.
If Iraqi leader Saddam Hussein had not been toppled by U.S. and British troops, his government would have been caught up in the same "Arab Spring" uprisings that later shook the region and now be embroiled in a bloody Syrian-style war, Blair said.
Blair spoke out as an offensive by insurgents that threatens to dismember Iraq seemed to slow after days of lightning advances as government forces regained some territory in counter-attacks, easing pressure on the Shi'ite-led government in Baghdad.
Blair, who heads a global political consultancy business, said the West would be pulled into the Iraq crisis whether it liked it or not, urging it to target Islamist extremists in Iraq and Syria with the agreement of Arab governments in the region.
"I'm not suggesting we put ground troops in and we do a full scale invasion as we did in Iraq or Afghanistan, but I am saying we are going to have to take an active role in trying to shape events in Syria and Iraq and indeed across the region," he said.
In Iraq's case, that action had to be immediate, he added, saying the selective use of air power was one option.
As leader of Britain's Labour party, Blair won three elections and was in office from 1997 to 2007. But the way he handled the Iraq war and the unfounded claims he and the United States made about the existence of weapons of mass destruction there - their casus belli - proved to be his political undoing.
Speaking from Abu Dhabi, Blair said on Sunday that the West's failure to take military action in Syria was one of the main reasons the Iraq crisis had bubbled up.
In an article on his web site, he said the Syrian conflict had given Islamist extremists a chance to rebuild and get military experience, saying there was a risk the country could become a more dangerous source of terror-related threats than Afghanistan in the 1990s.
He blamed the Iraqi government's sectarianism for the crisis too and said it had failed to use oil money to rebuild the country. Its army was inadequate, he added, questioning whether U.S. forces had withdrawn too soon.
The main reason the West had to intervene in Iraq and Syria was to protect its own security, Blair told BBC TV on Sunday.
"These people, if they are allowed to grow, these extremist groups, in the end they will pose a threat for us within our own borders," he said.