When President Trump hosted Canadian Prime Minister Mark Carney in the Oval Office, conversation turned not only to the relationship between the two countries, but to the border itself.
Echoing a phrase he has used in recent months, Trump described the U.S.-Canada border as an "artificially drawn line" — and suggested it should be erased.
"Somebody drew that line many years ago … like with a ruler, just a straight line right across the top of the country," Trump said at Tuesday's meeting. "When you look at that beautiful formation, when it's together — I'm a very artistic person — but when I looked at that beaut, I said, 'That's the way it was meant to be.' "
Trump: "To be honest with you, Canada only works as a state. We don't need anything they have. As a state it would be one of the great states. This would be the most incredible country visually. If you look at a map, they drew an artificial line right through it." pic.twitter.com/oxzF3jzLOC
— Aaron Rupar (@atrupar) March 13, 2025
Trump has set his sights on Canada since taking office, talking repeatedly of making it the 51st U.S. state. He also hit the country — one of the U.S.' top trading partners — with a 25% tariff on most goods, further antagonizing Canadians. That backlash is credited with propelling Carney — who campaigned on standing up to the president — to an unexpected election victory last month.
Carney told Trump that Canada is not for sale, and "won't be for sale, ever."
But by describing the boundary line as artificial, Trump seems to suggest otherwise, says Jon Parmenter, a history professor at Cornell University. He says the president's characterization of the border downplays "the fact that it has a complex, deep history and that it is an important part of everyday life on the North American continent."
"It's a real thing," says Parmenter, who teaches a class on the U.S.-Canada border. "And it concerns me, as a historian, to hear people dismissing it as something that's artificial … or in a sense, illegitimate."
Carney later told reporters he was "glad you could not tell what was going through my mind" during that conversation.
The U.S.-Canadian border is the longest international border in the world, stretching 5,525 miles across North America. Much of the border looks like a straight line because it essentially is: The line mostly follows the 49th parallel (of latitude north of the equator), while a smaller swath traces the 45th parallel.
The border is technically man-made: It was drawn on a map by the governments of America and Britain, which controlled Canada until 1867. In that way, Parmenter says, it — like all borders — is a construct.
"These are things that people decide makes sense at a particular moment in time," he says.
But just because it's not a naturally occurring border — like a mountain range or an ocean — doesn't mean it's not legitimate.
"The border is artificial in the sense that it's not something that … people living in proximity to it had any kind of role in making," he explains. "But it's not artificial in the sense that it's not real, and that it doesn't matter, and there aren't real-world consequences for traversing it in a manner that is deemed to be illicit."
How the border came to be
The U.S.-Canada boundary was shaped by a series of treaties that took place between 1783 and 1925.
The first was the Treaty of Paris, which ended the American Revolution, recognized American independence and set the Mississippi River as the western border of the new U.S. — which continued to expand throughout the 19th century.
Years later, the Convention of 1818 officially established the border between the U.S. and British North America — later Canada — at the 49th parallel, from Lake of the Woods, Minn., to the Rocky Mountains. The Oregon Treaty of 1846 extended the border to the Pacific Ocean.
"People sort of sat down and were going back and forth, and lines of latitude became the easiest way to resolve a dispute over who got what," Parmenter says.
Stephen Hornsby, a professor of geography and Canadian studies at the University of Maine, says the choice of the 49th parallel in particular was no coincidence.
The British wanted to preserve the northern part of the continent for the fur trade, while the U.S. wanted as much of the Mississippi basin as possible for agricultural settlement, Hornsby explains. They decided to split the land up based on the river systems, which at the time were the main way of traveling around the continent.
The 49th parallel, Hornsby says, made for an "extraordinarily convenient dividing line." Almost all of the rivers to the north flow out through the St. Lawrence River system or the Hudson Bay, while rivers to the south flow into the Mississippi River and Gulf of Mexico.
"Although it seems like a straight line across the land, when you start to look at the river systems and the larger watersheds, it's basically a dividing line between the watersheds north and south of that line," Hornsby says, adding that "it all makes perfect sense" on a map of North American river systems.
It didn't necessarily make perfect sense in real life, however. Parmenter says lines of latitude didn't take into account geographical formations or the traditional territories of Indigenous people already living there.
"There are Indigenous nations whose territories actually spanned what became the U.S.-Canada border, who come to find out when the survey happens, 'Oh, guess what, this is going right through the middle,' " he says. The Mohawk community of Akwesasne, in northern New York, is one example.
How the border is demarcated
Over the ensuing decades, as people moved westward and north, the U.S., the U.K., Canada and Russia negotiated some two dozen agreements, conventions and treaties to redefine the border, according to the International Boundary Commission (IBC) — which itself was created by treaty in 1908 to survey and map the border.
"It's a very piecemeal process," Parmenter says. "It sort of essentially is progressively drawn in a westward direction, but over time. So the Great Lakes area gets resolved, the prairie area gets resolved. The Pacific Coast and Alaska get resolved. And what you have left over is the longest international boundary on the face of the Earth, one that's a very diverse border."
Parmenter says there are various levels of "intensity and frequency of crossing as you go east to west." Some stretches of the border are actively monitored, including with helicopters and drones. But others, especially in remote areas, are marked only by monuments, like an obelisk or strategically placed rocks.
"In many places, it is a very permeable border," he says.
As part of its mission to tend the border, the IBC says it inspects and maintains over 8,000 monuments and reference points and 1,000 survey control stations. It also keeps a 20-foot wide treeless zone — called the vista — along the land boundary line.
"To make the boundary visible and unmistakable, we clear and maintain a swath called a vista that extends 10 feet on either side of the line through dense forests, over mountain ranges, across wetlands and highlands and some of the most rugged terrain North America has to offer," its website reads.
The vista, also called the Slash, mostly spans remote areas but is visible from certain land crossings, as well as Google Earth.
Where things stand
Parmenter, a dual U.S.-Canadian citizen, says, "People are on alert in Canada about this."
He says there is much more awareness of the border in Canada because such a high percentage of the population — by some estimates, as much as 90% — lives within 150 miles of it.
Proportionally, far fewer Americans deal with the northern border on a daily basis — and until recently have been much more focused on its southern border with Mexico, he says.
While the U.S.-Canada border has been stable for a century, it's also true that it was renegotiated multiple times in its early years. But Parmenter doesn't think that means a change is likely now, especially given Trump's tariffs and the overall state of affairs.
"It's always the case that in any relationship, things can get better, and I think that both sides would agree that there are some ways in which the management of this particular border could be improved," he says. "But the way to go about it is through sober and thoughtful negotiations, not ultimatums, not extreme rhetoric, not talk of annexation, because all that's done is to alienate Canadian people."
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