Above: Fortress North America: How Glorious? How Free? Tom Clark moderates a security town hall with Canada chief of defence staff and defence minister, and the U.S. national guard bureau general and NORAD commander.

HALIFAX — The old “Fortress North America” worldview has been getting increased attention as Canada and the United States both become targets of international terrorist threats.

The concept is a hangover from the Second World War and Cold War, a term used when imagining how Canada and the U.S. might operate if the rest of the world succumbed to communism.

Today, the threats lie in the increasingly violent ISIS and other terrorist groups. Canada came under attack last month when one radicalized Canadian killed a soldier in Saint-Jean-sur-Richelieu, Que. two days before a man shot and killed a second soldier who was standing guard at the National War Memorial in Ottawa. ISIS has taken credit for both attacks, writing in the most recent volume of its propaganda magazine, Dabiq, the attacks were the “direct result” of the group’s call for action against countries fighting it.

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In the meantime, Canada’s military is fighting alongside its coalition partners in Iraq, in an attempt to degrade and stop ISIS.

READ MORE: Halifax security forum and the idea of ‘Fortress North America’

The radical Islamic group is but one threat, one risk upon which North American officials responsible for safety and defence have their eyes.

U.S. National Guard Director Gen. Frank Grass said he is looking one to two decades down the road, where populations become even more concentrated in “megacities.”

“How are we going to take care of those people?” he asked during a Halifax International Security Forum panel discussion moderated by Tom Clark, host of Global TV’s The West Block with Tom Clark.

Of concern to Defence Minister Rob Nicholson is any impact attacks like those in October might have on the way North Americans live their lives he said.

READ MORE: Ottawa quietly taking another look at ballistic missile defence

“We don’t want them to change our lives,” he said during the panel. “We don’t want them to change the kind of society that we grow up in. I worry about that, but this is the challenge that we have to meet.”

Those concerns led to the question, the topic of the panel discussion: What benefit, if any, would a “Fortress North America” afford the citizens and governments of the U.S., Mexico and Canada?

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None of the panelists on stage, which included Canada’s Chief of Defence Staff Gen. Tom Lawson and NORAD Commander Gen. Charles Jacoby, doubted the advantages North American countries reap from working together.

WACTH: Canada’s Defence Minister Rob Nicholson says the House of Commons is considering a Senate report urging the government to join the U.S. ballistic missile defence system.

But the idea of a “fortress” might work against the very principle the concept is trying to promote, said Lawson.

“What would keep me awake at night is the sense that Canada might develop some sort of complacency that would come along with a notion of Canada being part of a fortress,” he said. “A fortress gives the sense of walls, keeping away all threats when, in fact, we’re anything but.”

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Any such complacency, Lawson said, might lead to a public, government and military at ease — a state of mind and activity that effectively ignores the fact, highlighted in October’s attacks, many threats already exist within our borders.

“Those were radicalized Canadians,” Lawson said of the attackers in Quebec and Ottawa. “They did not come from the outside. They were not going to be stopped by any fortress walls … I think we have to recognize that any sense of fortress really is broken down when we understand that many of the threats are already within.”

READ MORE: Blame it on Bush? Former defence ministers explain why ballistic missile defence was denied

If North American countries don’t erect figurative walls to block out external threats and contain what’s within, what’s the answer?

We can’t ignore the efforts and actions the three countries together have already taken, Nicholson said, pointing to the Joint Board on Defence established in 1940 and NORAD in the late 1950s.

“There’s been a long-time recognition that there is no threat to the United States that is not a threat to Canada or vice versa,” he said. “We understand that, and I think that this has been in place and when you see attacks like we have seen, this reinforces and makes the case for the importance of that relationship between the two countries.”

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In attendance at the conference was the largest congressional delegation ever to come to Canada, which included Arizona Sen. John McCain and Virginia Sen. Tim Kaine, both of who endorsed the idea of the fortress and greater integration.

READ MORE: Canadian Forces vet Dillon Hillier plans to fight ISIS with Peshmerga

“There is very little doubt of what the intentions of ISIS are and other terrorist organizations,” McCain said. “I don’t think there is any doubt that our director of national intelligence, the director of the CIA and our director of homeland security have all stated that ISIS, over time, poses a direct threat to the U.S. and that of course means Canada as well.”

Kaine, meanwhile, said he can’t see any downsides to greater integration. The only “quibble,” he said, is using the word “fortress.”

“I want to find a better word,” he said. “Fortress to me kind of conveys a little bit of an inward looking. We put up the wall and we try to avoid penetration from outside. We have so much to offer the world on the offence side in values, trade and culture.”

WATCH: U.S. Senators Tim Kaine and John McCain join the discussion, weighing in on the greatest threats to the continent’s security.

Discussions of North American integration often elicit talks of the ballistic missile defence system, which, in 2005, Canada chose to not participate with the U.S.

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During the panel, Nicholson admitted the issue was raised again recently with a Senate report unanimously recommending Canada’s leaders consider a ballistic missile defence system.

The minister said he is taking the recommendations into consideration, as well as the opinions of MPs in the House of Commons but “there is no decision or change to that decision at the present time.”

Jacoby, the NORAD commander, however, noted there are real, current threats warranting attention.

“North Korea now must be considered a practical threat to North America for attack by [intercontinental ballistic missiles] with weapons of mass destruction,” he said, adding he understands the intent and design of Iran is to achieve the same capabilities.

“I think the proliferation of mass destruction technologies keep that door open for other threats to emerge as well. So I believe that missile defence is important for the United States. It’s important for the continent.”