The idea of a war between Canada and the United States was inconceivable even a few months ago. Most Americans still don’t believe it’s a possibility, or simply haven’t noticed their president’s occupationist rhetoric, or can’t imagine a world in which a neighbor they have been at peace with for 150 years is suddenly an enemy. The very idea seems completely absurd.

But Canada does not have the luxury of dismissing White House rhetoric as trolling. Canadians are imagining the unimaginable because they have to.

Donald Trump’s pointless and malicious trade war has been, by his own account, a prelude to softening up Canada economically so that it can be appropriated as the 51st state. He has brought up his plans for incorporating Canada into the union with Prime Ministers Justin Trudeau and Mark Carney in private calls. The definitive end of the status quo came with the president’s casual comment that he would sell only deliberately downgraded F-47s to allies who purchased American military hardware, “because someday, maybe they’re not our allies.” From that point on, spending on equipment from the American military-industrial complex is a form of national suicide for any country in the free world. Canada could no longer comfortably sit within the American military sphere.

In this stark moment, our nation has abruptly become an adversary of the most powerful country in the world.

An American military threat is Canada’s worst nightmare. And Canada is unprepared precisely because it never considered the U.S. to be a potential threat. Trust made Canada vulnerable. For 60 years at least, both Conservative and Liberal governments have worked toward greater integration with the United States. Our country’s trade and security policies have been built on the premise of American sanity. That assumption, it turned out, was a mistake, hopefully not a fatal one.

What would a continental conflict look like? Conventional war between the United States and Canada would be highly asymmetric, to say the least. The U.S. possesses an enormous military, comprising more than a million men and women under arms. Canada’s armed forces have 72,000 active members. Even worse, because of its deep-seated trust in the United States, Canada has built its forces around interoperability with U.S. forces, both for mutual continental protection, in binational projects such as the North American Aerospace Defense Command (NORAD), and for expeditionary forces such as the NATO mission to Afghanistan.

This vulnerability does not mean that Canada would be there for the taking. “The U.S. military does not have the capacity to seize the country,” Scott Clancy, who served as a Colorado-based director of operations for NORAD, told me recently. Clancy served 37 years in the Royal Canadian Air Force and rose to the rank of major-general, and is intimately familiar with U.S. and Canadian military capabilities. “They would have to seize specific points. And the more they went into cities, the more it would become unmanageable from an American military point of view.” A continental war would, then, likely play out as an insurgent conflict in Canadian North America—and across the U.S. homeland, as well. “Let’s say they just hold the oil fields,” Clancy said, referring to a U.S. military occupation of Canadian oil reserves. “We’re not gonna roll over. And just because you attacked Alberta doesn’t mean that we’re not gonna strike at you in New York.”

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When I interviewed half a dozen experts on insurgent conflict for my book The Next Civil War, they all agreed that insurgent conflict was the least predictable and containable. Aisha Ahmad, a political-science professor at the University of Toronto, told me she does not think Canada’s reputation for gentleness would make it any less brutal as an opponent. “There’s no such thing as a warrior race,” said Ahmad, who is an expert on insurgency who has conducted field work in Afghanistan, Pakistan, Somalia, Lebanon, Mali, and Kenya. “Nobody is born an insurgent. Insurgency is what happens when someone kills your mom.” Just one soldier firing on a protester at a rally could be the spark. “All of these cute, latte-drinking TikToker students,” she said. “You look at them and you don’t see insurgents. But if you kill their moms, the Geneva Convention will not save you.”

An occupying military force has three strategies for dealing with insurgent conflicts, none of which work. The first we could call “Groznification”: complete suppression, as the Russian army did in Chechnya at the turn of the century. Even the destruction of any means of resistance works only temporarily, as Colonel Gaddafi learned in Libya. “Hearts and minds,” the strategy applied in Iraq and Afghanistan, is also ineffective: If you build hospitals and then fill them with corpses, you just generate more insurgents. The third option is “decapitation,” but the systematic targeting of insurgent networks’ leaders—the idea behind the recent U.S. air strikes on the Houthis in Yemen—can easily be countered by detailed succession plans. And killing leadership has the unintended consequence of fragmenting the insurgency’s power structures, so that, if you ever do want to negotiate a peaceful settlement, you have dozens of mini-insurgencies to deal with, rather than a single contained force.

The Canadian population would present particular challenges to any counterinsurgency strategy. “The Taliban would look lightweight,” Ahmad told me. “Canada has all of the attributes to have an even fiercer insurgency than the other places in the world where I study these problems.” Canada has the most educated population in the Group of Seven advanced industrial nations, which for a resistance movement would be “an asset in being able to identify pressure points, in being able to know what critical infrastructure is, in being able to develop technology and weapons that can be highly disruptive,” Ahmad said. “The scale and the capacity would be so much higher.” If only one in 100 Canadians took up arms against an American occupation, that force would be 10 times the estimated size of the Taliban at the outset of the Afghan War. And that force would consist of machine-learning specialists and petroleum engineers rather than shepherds and subsistence farmers.

Canadians are already a well-armed population. More than a quarter of Canadian households own a gun. Consider, also, the Canadian landscape, which is vast beyond imagination and would provide ideal cover for insurgents. To give you an idea of that wilderness, Manitoba alone, one of 10 Canadian provinces, has some 90,000 unnamed lakes—even Canadians can’t keep track of their territory.

In short, a continental conflict would be an unmitigated act of murderous folly. But murderous folly is not beyond the capacity of this new iteration of the United States.

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Already, the once-unthinkable idea of a war between Canada and the United States is growing less unthinkable. Before the 2024 U.S. election, 12 percent of Republicans viewed Canadians as “unfriendly” or “an enemy.” Now that number is 27 percent. Persuading the military to carry out an attack on Canada would probably be more difficult than convincing the population to support such an attack. The American officer class is trained, from the beginning, in “the duty not to follow orders,” and combat operations against Canada would involve fighting against fellow soldiers who shed blood beside them in Afghanistan and other theaters. Canadian and American soldiers have attended a great number of one another’s funerals.

But turning the U.S. military is far from impossible. The Trump administration fired the commander of a Space Force base in Greenland the moment she expressed a position wavering from his annexationist aims there. The Naval Academy has already purged its library and canceled various speakers. At least some of the U.S. military’s leaders are on board with the ideological purification of their institutions.

The conditions required for the occupation of Canada would also mean the end of American democracy. That, too, is not an impossible outcome—and a U.S. military adventure might even have both objectives in view. “The orchestration of a security crisis allows the incumbent government to declare emergency powers and bypass ordinary politics,” Ahmad said. “The Trump administration has already signaled that it wants a third term.” The 2028 election will be a watershed. If Trump decides to run again, a manufactured emergency over Canada would be a convenient excuse for overturning the constitutional barriers.

Nobody wants to believe that a continental conflict could happen. Very few Ukrainians, right up until the point of Russia’s 2022 invasion, believed that their malignant neighbor would invade. Canadians cannot afford complacency.

Reflecting on U.S.-Canadian relations in happier times, President John F. Kennedy said: “Geography has made us neighbors. History has made us friends. Economics has made us partners. And necessity has made us allies. Those whom nature hath so joined together, let no man put asunder.” Now, and for the foreseeable future, Trump has sundered us. And yet, even so, our fates remain entwined. The end of America would destroy Canada. The occupation of Canada would destroy America.