Tony Blair has defended Britain's involvement in Iraq and Afghanistan, by arguing that only an interventionist stance can confront terrorism head-on.
What happened in those countries was crucial for UK security. "This is not a clash between civilisations, but a clash about civilisation," he said.
He attacked those against his vision of an "activist" foreign policy, saying this was a battle about "modernity".
His speech, in London, was the first of three on foreign policy and terrorism.
Values and ideas
It comes three years after bombs started dropping on Baghdad at the start of the US-led campaign that resulted in the fall and eventual capture of former Iraqi President Saddam Hussein.
Mr Blair insisted that controversial military operations in Iraq and Afghanistan were not distant entanglements but essential to Britain's future security.
"We must reject the thought that somehow we are the authors of our own distress, that if only we altered this decision or that, this extremism would fade away," he said.
"In my judgement, the only way to win is to recognise this phenomenon is indeed a global ideology, to see all areas in which it operates as linked and to defeat it by values and ideas set in opposition to those of the terrorists."
He told the audience at a Reuters event that religious extremism - including the term Islamist extremism - should be labelled as such.
"It will give offence. It is true. It will," he said.
But he said Muslims who committed acts of terrorism were no more true to their faith than the "Protestant bigot" who murdered Catholics in Northern Ireland.
"But unfortunately he is still a Protestant bigot. To say his religion is irrelevant is both completely to misunderstand his motive and to refuse to face up the strain of extremism within his religion that has given rise to it."
Mr Blair said terrorism "will not be defeated until its ideas, the poison that warps the minds, its adherence, are confronted at their essence, at their core".
"We are not 'the west', we are as much Muslim and Christian or Jew or Hindu," he said.
"We are those who believe in religious tolerance, openness to others to democracy, liberty and humanitarianism, administered by secular courts.
"It will not be defeated until its ideas are confronted head-on, on its absurd anti-Americanism, absurd pre-feudal concept of government and its position on women and other faiths.
"The only way to win is to recognise this phenomenon is a global ideology, to see all the areas where it operates and to defeat it by values and ideas set in opposition to those of the terrorists."
He said terrorists know that if they can succeed in Iraq, Afghanistan or the Lebanon - who want to go down the democratic route - then the choice of a modern future for the Arab or Muslim world is "dealt a potentially mortal blow".
"Likewise, if they fail and these countries become democracies and make progress then not merely is that a blow against their own value system, but it is the most effective message against their wretched propaganda about America, the west and the rest of the world."
Mr Blair's speech comes after the British deputy commander of all the multi-national forces in Iraq, General Sir Rob Fry, rejected claims that Iraq was in a state of civil war.
At the weekend, the former Iraqi interim prime minister, Iyad Allawi, claimed his country was in the grip of a civil conflict.
"I'd describe the situation as very difficult and I think we're in the middle of an intractable sectarian conflict but we're certainly not in civil war," said General Fry.
Mr Blair also launched a broadside on sections of the media who he accused of sitting back and arguing that stability in the world would be promoted by doing nothing.
He claimed they were guilty of "a superficial deal with extremism", adding that such behaviour must "be confronted and uprooted".
Liberal Democrat leader Sir Menzies Campbell said Mr Blair should use his future foreign policy speeches to announce an inquiry into the decision behind the Iraq war "and to apologise".
US President George W Bush, meanwhile, has marked the anniversary of the start of the campaign in Iraq with an upbeat assessment of the country's prospects.
Iraqis in some areas still faced "savage" acts of violence, Mr Bush said, but he insisted that insurgents were being defeated in many places.
"The decision to remove Saddam Hussein was the right decision," he said in a speech in Cleveland, Ohio.