Over the past few weeks, basic geopolitical facts —that the United States would not forcibly expand its borders or that a NATO member state would never invade another member state—have become suddenly unsettled, thanks almost entirely to U.S. President Donald Trump’s ongoing threats against Greenland. It has all been, as Canadian Prime Minister Mark Carney recently said, a “rupture,” a moment in which an old order collapses and a new one struggles to be born.

While much of the attention has focused on the fracture in trans-Atlantic relations, much of that rupture has centered on something far closer to home for Carney: U.S.-Canada relations. Because it’s not just Denmark or Greenland that is suddenly realizing Washington under Trump is now a threat. It is also Canada, which is now witnessing a U.S. government openly menacing not only Canadian sovereignty but even Canadian nationhood itself. Trump has himself threatened Canada time and again, calling for the US to absorb Canada and repeatedly suggesting that the border between the two nations should be erased. Nor is this just idle chatter; just last week we learned that that Trump administration officials had begun meeting directly with separatists in Alberta, who are keen to break their province off of Canada and attach it to the US.

Over the past few weeks, basic geopolitical facts —that the United States would not forcibly expand its borders or that a NATO member state would never invade another member state—have become suddenly unsettled, thanks almost entirely to U.S. President Donald Trump’s ongoing threats against Greenland. It has all been, as Canadian Prime Minister Mark Carney recently said, a “rupture,” a moment in which an old order collapses and a new one struggles to be born.

While much of the attention has focused on the fracture in trans-Atlantic relations, much of that rupture has centered on something far closer to home for Carney: U.S.-Canada relations. Because it’s not just Denmark or Greenland that is suddenly realizing Washington under Trump is now a threat. It is also Canada, which is now witnessing a U.S. government openly menacing not only Canadian sovereignty but even Canadian nationhood itself. Trump has himself threatened Canada time and again, calling for the US to absorb Canada and repeatedly suggesting that the border between the two nations should be erased. Nor is this just idle chatter; just last week we learned that that Trump administration officials had begun meeting directly with separatists in Alberta, who are keen to break their province off of Canada and attach it to the US.

The days of laughing off Trump’s threats of turning Canada into the 51st U.S. state are long past. A new reality has suddenly rippled across Canada: that the United States under Trump is, as strange as it may be to stomach, suddenly Canada’s largest national security threat.

It is a reality that Canadians are finally beginning to adapt to. But it is also a reality that taps into a far longer, far deeper vein of U.S. peril facing Canada. Indeed, the past 80 or so years of U.S.-Canada comity—in which the world’s longest border was largely peaceable and in which Washington and Ottawa became perhaps the closest allies in the entire world—may increasingly seem like an anachronism, an anomaly in which the United States simply paused on its far broader history of expansion in North America.

If anything, the United States under Trump is returning to its traditional position as a nation willing to intimidate its northern neighbor, preferring brutish expansion to stable alliance—even to the point of disappearing Canada from the map entirely. That history is largely overlooked in the United States but is worth considering if Washington is ever to become a trusted partner once more—and if we’re ever to see a stable North America again.

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The history of the United States coveting Canadian territory goes back to the earliest days of the country itself. In 1774, the nascent Continental Congress in Philadelphia wrote a letter to Canadians, claiming that they were a “small people” and inviting them to join the burgeoning efforts to throw off British control. The invitation came laced with menace, saying that Canadians should consider whether they wanted “all the rest of North-America [as] your unalterable friends, or your inveterate enemies.” If Canadians declined to join American colonists, they would be, the letter added, “conquered into liberty.”

Nor was this some kind of fringe position. “The Unanimous Voice of the Continent is Canada must be ours,” future U.S. President John Adams wrote in 1776. “Quebec must be taken.” Benjamin Franklin likewise eyed Canada as future U.S. territory; as Canadian historian Madelaine Drohan discovered, Franklin pushed for either forced assimilation or outright eviction of French Canadians (who were then nearly the entirety of the European colonial population in Canada), with the United States then reigning over all of British North America.

Of course, these early positions were all for naught. U.S. forces launched a disastrous assault on Quebec, undone by both poor strategy and smallpox alike. Franklin’s attempts to seize Canada during resulting negotiations with Britain also failed. As Adams himself wrote, “Alass Canada! We have found Misfortune and disgrace in that Quarter.”

Those failings, however, didn’t end U.S. designs on Canada. During the War of 1812, U.S. forces once more had British Canada in their sights, with one general saying that Canada would be “one of the United States.” Canadian annexation may not have been the outright goal of the broader fighting, but the war itself—which expelled British forts from much of central North America and all but ended British barriers to U.S. expansionism—cemented an image of the United States as a thrusting, grabbing power that would quickly race toward continental dominance.

That reality came to the fore in the mid-19th century, at the height of the United States’ continental imperialism. During ongoing disputes over the Oregon Territory, then jointly managed as a British-American condominium, U.S. presidential candidate James Polk’s backers regularly cheered, “Fifty-Four Forty or Fight!” as a means of convincing British Canada to give up sovereignty over everything in the Pacific Northwest up to the 54th parallel. Polk eventually balked on outright war, securing U.S. sovereignty up to the 49th parallel (and focusing instead on carving up Mexico). Still, Polk’s imperialist supporters didn’t stop; as John O’Sullivan, the reported author of the phrase “Manifest Destiny,” wrote, it remained the country’s “manifest destiny to overspread the continent allotted by Providence”—including Canadian territory.

Even the Civil War, rending the United States and leading to the slaughter of hundreds of thousands of Americans, did little to stop U.S. designs on Canada. Immediately following the war’s conclusion, the United States finalized the Alaska Purchase, obtaining the territory from tsarist Russia. The purchase, however, didn’t exist in a geopolitical vacuum; Secretary of State William Seward, who spearheaded the purchase, saw U.S.-controlled Alaska as the key to gaining British Columbia as well, and potentially far more. “Nature designs that this whole continent … shall be, sooner or later, within the magic circle of the American Union,” Seward told an audience in 1867. As the University of Virginia’s Alan Taylor writes in his magisterial history of the era, “Americans celebrated the [Alaska] acquisition as a squeeze play on Canada.” All they had to do was wait, and Canada could be theirs.

Canadians, however, went in a different direction. Instead of fracturing Canada, the Alaska Purchase resulted directly in the cohering of a sovereign Canada and an entirely independent Canadian identity. Shepherded by leaders such as John Macdonald, Canadians launched a nationwide confederation, adding province after province to the new Dominion of Canada in the coming years. Rather than fall prey to U.S. annexationists, Canada consolidated, blunting further U.S. expansion and cementing an independent nationhood that has continued for more than 150 years.

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All of these elements—the Founding Fathers’ claims to Canada; the throughlines of U.S. threats against their northern neighbor; Canadian consolidation in the face of the U.S. threat—were, until very recently, fascinating historical footnotes, snapshots of different, more turbulent eras. Even as U.S. politicians threatened potential war in the 1890s, even as they continued calling for the “American flag [to] float over every square foot” of Canada in the 1910s, and even as Washington drew up contingency war plans against Canada in the 1930s, actual U.S. threats against Canadian sovereignty largely receded. Indeed, the U.S.-Canada partnership grew so close that successful relations were eventually taken for granted. The tightest partnership Washington maintained faded into something like background noise, with a stable North American security architecture allowing the United States to expand its global dominance.

And then it all fell apart. Trump’s threats against Greenland have paralleled threats against Canada; indeed, even at the height of the Greenland crisis, NBC News reported that Trump was “privately ramping up his focus” on Canada, even to the point of showing maps of Canada with a U.S. flag draped over it. All of this comes in addition to the fact that, as Canadians well recognize, Trump’s rhetoric about Greenland—that only the United States can defend it and that Denmark has no right to it, anyway—could just as easily apply to Canada’s Arctic islands, many of which abut Greenland itself.

Nor is Trump alone. MAGA ideologue Steve Bannon has vocally called, time and again, for U.S. suzerainty over Canada. Bannon recently said the “Arctic north, which used to be Canada’s great barrier—it’s now their biggest exposure,” claiming it as the country’s “soft underbelly.” As Bannon continued, Canada “could be the next Ukraine”—one that is full of “people [who] are hostile to the United States.” And it’s not just the Arctic; this week, the Financial Timesreported that Trump administration officials met on multiple occasions directly with far-right separatists in Alberta, who have made no effort to conceal their desires to join the United States.

A neoimperialist power seeking to expand its borders and inflame nearby separatist movements, all as a means of asserting regional dominance and potentially cleaving apart neighboring states—indeed, the parallels between Canada and Ukraine are growing uncomfortably close. But Canadians, just as Ukrainians before them, are hardly taking this all lying down. Canada’s Department of National Defence has begun plotting out a new civilian defense force, and for the first time in a century, Ottawa has started planning war games to model responses to U.S. aggression.

And Canadian officials are finally, and publicly, sounding the alarm. U.S. threats against Canada are “existential,” Bob Rae, a former Canadian ambassador to the United Nations, told the Globe and Mail, with a former Canadian defense chief saying Trump’s moves should put Canada on high alert. As one Canadian conflict researcher told the Guardian, “We’ve been critically dependent on the friendship and benignness of the United States, and all of a sudden, both those things have just disappeared. They’ve vanished, and I worry that only now Canadians fully appreciate what this means.” It’s all a shock and a sign that whatever stability once existed in North America can longer be taken for granted. Everything from NORAD to icebreaker fleets to intelligence gathering is suddenly an open question—as is even Canadian territorial integrity itself.

Then again, as Trump is almost certainly unaware, Canada has a far deeper history of beating back U.S. designs than most outside Canada have ever known. That history is far more relevant now than it has been in a century—all thanks to a rupture that is only just beginning.