He added that experience from conflicts in Iraq and Libya showed "dealing with the dictator" was not enough in the "wider battle against extremism".
Extra RAF fighters have been deployed to bomb IS targets in Syria after MPs backed air strikes on Wednesday.
Two Typhoons and a pair of Tornados were seen leaving the RAF base at Akrotiri in Cyprus on Friday, although details of their mission have not been released.
On Thursday, Tornados struck at six targets belonging to IS, which the government refers to as Daesh and has also been referred to as Isis and Isil.
Mr Blair told the BBC`s Katty Kay: "Even if we thought we could stay out of Syria we can`t because our own interests are dramatically involved."
He said the Paris attacks on 13 November had showed that if IS was given the opportunity to "gain strength", it would come to Europe and the US and target Westerners.
But he said the Syrian conflict was different to those in Iraq and Afghanistan because the UK and US now had allies in the region.
"Whereas post 9/11 a lot of countries in the region tended to think `well this is your problem, you`re dealing with it`, today all of those countries have got their own issues of extremism, their own problems that they`re fighting," he said.
"They see the opportunity now for an alliance, and we have an opportunity for an alliance that wasn`t there before."
Mr Blair has previously apologised for mistakes made over the 2003 Iraq War - and said there were "elements of truth" in claims that it caused the rise of Islamic State.
He said the West had previously tried to "deal with the dictator" within conflicts.
"In the end I`m afraid those countries out in that region, the young populations who are frustrated, deprived of opportunity, they`re not going to tolerate that so inevitably we are going to have to be involved and the question is how do we get involved most sensibly," he said.
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