Canada is now at war in Syria.

Prime Minister Stephen Harper used his party's Commons majority to authorize extending Canada's military fight against Islamic State militants in Iraq for 12 months and expanding that fight into Syria.

The Commons vote took place in a divided House where Canada's two major opposition parties, with about 40 per cent of the seats, refused to support it. The Commons motion endorsing the revised mission passed 142-129. Thirty-three MPs were absent for the vote and one abstained.

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CF-18 fighters are preparing to begin dropping bombs inside Syria shortly, with one government source saying this could begin "in a matter of days."

Mr. Harper did not speak to reporters after the vote but put out a statement defending his government's position.

"While the coalition [fighting the militants] has succeeded in stopping ISIL territorial spread, the global threat that ISIL poses remains," said Mr. Harper, referring to another acronym for IS militants. "In particular, we cannot stand on the sidelines while ISIL continues to promote terrorism in Canada as well as against our allies and partners, nor can we allow ISIL to have a safe haven in Syria."

The new mission gives Canada a higher profile role as the only Western nation joining the United States in bombing Syria, but also thrusts the Canadian Armed Forces into a more risky and morally murky conflict. Unlike Iraq, Syria has not invited Canada to wage war inside its borders.

Canadian pilots will be further from help if their planes crash in Syria, where there is no ground support, and the air strikes inadvertently put Canada on the same side as the Bashar al-Assad regime that rules Syria despite an odious international reputation for a murderous war on its citizens.

Last October, Mr. Harper promised he wouldn't conduct air raids inside Syria without the consent of the Assad government.

But last week, the Prime Minister said he'd changed his mind after watching Islamic State forces seeking safe haven there from the larger-scale aerial bombardment in Iraq.

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The Conservatives have framed the expanded and extended mission as a matter of national interest, saying Islamic State poses a direct threat to Canada because it has urged jihadists to launch attacks here – a threat opposition parties have questioned.

"It is clear that part of their ideology extends to projecting their force, projecting their terror, projecting their violence on our peaceable shores, as well," Treasury Board President Tony Clement said Monday of Islamic State.

The Harper government has also increasingly justified this deployment – which has taken the life of one Canadian soldier and cost more than $120-million – by saying Canada has a "responsibility to protect" Iraq from jihadists who are taking refuge in Syria but whom Damascus appears unwilling or unable to control.

The mission includes six CF-18 warplanes, two surveillance aircraft and an aerial refueler, with about 600 support staff operating out of Kuwait, as well as 69 special forces soldiers advising Kurdish fighters in northern Iraq.

The federal government said it will shortly notify the United Nations by letter – as the Obama administration did – and cite Article 51 of the UN Charter, the self-defence clause that says a country can take individual or collective action on behalf of a member under armed attack.

Mr. Harper declined to say how long it might take to dismantle the threat posed by Islamic State, which last year cut a swath of destruction across Syria and Iraq using brutal violence and slaughter that the UN has said constitute war crimes.

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"Can I promise that this objective will be attained in two years? the Prime Minister said Monday afternoon during a press conference in Alliston, Ont. "That's not certain. But obviously all our partners are committed and it is essential for the security of our country and of Canadians."

The U.S. government applauded Canada's decision to join the fight inside Syria. To date, other NATO allies including Britain, France and the Netherlands, have restricted their air strikes in aid of Iraqi and Kurdish forces to targets in Iraq, which asked for help.

"Canada has long played a vital role in efforts to degrade and defeat ISIL and I would like to express my appreciation on behalf of the United States government and the American people for its decision to continue its important contribution to the anti-ISIL coalition," said Ambassador Bruce Heyman.

NDP Leader Tom Mulcair, who promises to bring the troops home if elected next fall, said Canada's war contribution is only a token response and that the money should be better spent focusing on delivering humanitarian aid to the millions of people affected by Islamic State's brutal reign.

"The Americans have been fighting in Iraq for over a decade with very little success," Mr. Mulcair said. "Canada should have no part in it. We were right to stay out of the fight in 2003."

Liberal Leader Justin Trudeau promised to sponsor 25,000 Syrian refugees if he wins power in the next election, expected this October, saying the fight against the Islamic State needs more effort on addressing "the root causes" of radicalization "including poor governance and lack of economic opportunity."

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He acknowledged public support seems to support a Canadian role in the war. "Canadians did not send us to this House to read polls and guess at what they want. They did not put us here to stick a finger in the wind and follow whichever way it seems to be blowing," Mr. Trudeau said.

Liberal MP Irwin Cotler issued a statement saying he would abstain from the vote, explaining that he believes in the doctrine of responsibility to protect but feels Canada's bombing within Syria would take pressure off Damascus and "allow Assad to assault Syrian civilians with impunity."

Independent Brent Rathgeber, a former Conservative MP, voted against the mission. Green Party Leader Elizabeth May also voted against, as did Green MP Bruce Hyer. Independent MP Scott Andrews, recently suspended from the Liberal caucus, voted in favour.