Tony Blair denied colonialism was to blame for radical Islam
Tony Blair has said the case for using military force to topple oppressive regimes is as strong as it ever was - despite events in Iraq and Afghanistan.
He said intervention was needed to tackle the growing "menace" of Islamic "extremism" across the Middle East.
But he also stressed the need for engagement with "progressive" Muslims.
The former prime minister was speaking on the 10th anniversary of a speech in Chicago which he set out his belief in an interventionist foreign policy.
In April 1999, during the Kosovo conflict, Mr Blair outlined his criteria for military action abroad in an address to the Chicago Economic Club.
Returning to the city this week, he told the Chicago Council on Global Affairs: "Many, at the time, described the speech as hopelessly idealistic; dangerous even.
"And, probably, in the light of events since then, some would feel vindicated.
"As for me, I am older, better educated by the events that shaped my premiership, but I still believe that those who oppress and brutalise their citizens are better put out of power than kept in it."
Events in Iraq and Afghanistan had shaken the "familiar certainty that our power would always triumph", argued Mr Blair.
He said it would be wrong to revert to a "more traditional foreign policy" which he described as "less bold, more cautious; less idealistic, more pragmatic, more willing to tolerate the intolerable".
But he said a broader strategy was needed to deal with the threats posed by extremism.
"Back in April 1999, I thought that removal of a despotic regime was almost sufficient in itself to create the conditions for progress. But this battle cannot so easily be won.
"Because it is based on an ideology and because its roots are deep, so our strategy for victory has to be broader, more comprehensive but also more sharply defined.
"It is important to recognise that it is not going to be won except over a prolonged period.
"In this sense, it is more akin to fighting revolutionary Communism than a discrete campaign such as the one which changed the Balkans a decade ago."
He stressed the importance of supporting moderate Muslims, but also of confronting radical Islamic thinking through a "consistent critique of its religious error".
And he spoke of the role he hoped to play in developing a dialogue between different religious groups, through his Tony Blair Faith Foundation.
In an interview with the BBC, Mr Blair described extemism as a genuine "menace", the scope of which "stretches very wide" across the Middle East.
He said extremists needed to know that the international community "will do whatever is necessary to defeat them" including, but not limited to, military action.
Mr Blair added: "The cause is not British colonialism from years ago or the creation of the state of Israel.
"There is an extremism that has grown up over decades that will have to be confronted, possibly over decades.
"We've got to stick to what we believe, and take it on by the combination - not just military and security means - but of diplomatic initiatives that allow us, together with those sensible and progressive forces within Islam, to uproot the extremism and eradicate it."
But he rejected the idea of military action in Pakistan, arguing instead for a more subtle approach.
He said: "We need to start working on some of the root causes of this, for example deep within the Pakistani education system, the way kids are brought up and taught.
"We need to get those clerics and thinkers within the world of Islam, who have got in fact a far more accurate and true view of what Islam is about, to be speaking out, to be given the ability to influence people's minds because otherwise we will be in a situation where whatever military action we take there is a continual growth of this extremism in countries like Pakistan and elsewhere."