French President Francois Hollande has firmly condemned the Nov. 13 attacks in Paris as an "act of war," and promised "merciless" revenge.

The decisive response puts pressure on France's NATO allies – including Canada – to support Hollande.

But despite the president's use of the term, it's still unclear if supporting France means Canada is obligated to go to "war."

As France intensifies its airstrikes on targets in Syria, here's a look at how the Paris attacks could affect NATO's role in Syria:

What is Article 5?

NATO's response to the attacks could hinge on a formal invocation of Article 5 of the North Atlantic Treaty, University of Toronto International Relations Professor Aurel Braun says.

In the treaty, Article 5 reads: "The Parties agree that an armed attack against one or more of them in Europe or North America shall be considered an attack against them all and … (they) will assist … (with) such action as it deems necessary, including the use of armed force, to restore and maintain the security of the North Atlantic area."

According to Braun, if France invokes Article 5, its NATO allies are obligated to respond.

"Article 5 commits members of the alliance to come to the defence of anyone who has been attacked," Braun said on CTV's Canada AM on Tuesday. "They're supposed to bring whatever resources they can and mobilize those resources in order to beat an attacker."

Is France likely to invoke the article?

Braun says it "wouldn't be unusual" for NATO to invoke Article 5 after attacks such as the ones in Paris.

But that doesn't mean that it is guaranteed to do so.

Article 5 has only been used once in the past, after the 9/11 attacks in the United States. And while invoking the article would bring more resources and strength to the French fight, Braun said the situation in Syria remains extremely complex.

A U.S.-led coalition is currently conducting airstrikes in Iraq and Syria.

But the coalition countries are not there as part of a NATO or UN-mandated mission, and the United States has been reluctant to fully commit to on-the-ground intervention, Braun said.

Because of this, invoking Article 5 and forcing action could strain the relationship between Hollande and U.S. President Obama.

"It's complicated," he said. "If they (France) invoke the article they have to make sure that the U.S., in particular, agrees to it.

If the Americans are reluctant to provide as much help as France wants, it's going to fray the alliance. This is why I'm not entirely convinced that they will invoke the article."

How much of a threat does the Islamic State pose to the NATO countries?

According to Braun, the Islamic State militants should not be underestimated.

"Despite the fact that President Obama kind of said, 'well this is sort of a B team, they're amateurs,' a little while ago, the Islamic State now controls an area that is about the size of Britain," he said. "It has enormous resources."

Braun said the attacks in Paris and bombing of a Russian plane prove that the Islamic State is a significant force that needs to be addressed.

Does this mean Canada will have to commit ground troops?

No, not necessarily.

Article 5 states that allies should take "such action as it deems necessary," to protect each other. And while the treaty says these actions could include "the use of armed force," it doesn't necessarily mandate it.

Prime Minister Justin Trudeau is currently moving forward with a plan to withdraw Canadian fighter jets from the fight against the Islamic State, but he says Canada will continue to support the fight by supplying training for local fighters.

On Tuesday, he announced that Canada will send an unspecified number of additional trainers to Iraq to join the 69 special forces members who are already there.

But are training and airstrikes enough to defeat the Islamic State militants?

In Braun's opinion, defeating Islamic State militants will take more than selective airstrikes or training local forces.

"When you say 'we're going to have trainers,' well, we have been trying to train collectively the Iraqi forces and they've proven to be absolutely useless," he said.

Instead, Braun said France and its allies need a "comprehensive" strategy, and must be prepared for a long-term commitment, multiple contingencies, and sacrifice.

"War cannot be fought on the cheap," Braun said. "It is horrific, it is costly, (and) it needs a larger strategy."