Is Donald Trump right when he says the border is just an 'artificially drawn line'?

U.S. President Donald Trump repeated one of his favourite talking points in his meeting with Prime Minister Mark Carney Tuesday, saying the Canada-U.S. border is an "artificially drawn line." 

"Somebody drew that line many years ago with, like, a ruler — just a straight line right across the top of the country," he said when the two leaders met in front of reporters at the White House.

When a reporter later asked Carney what he was thinking when Trump made the comment, the prime minister quipped, "I'm glad that you couldn't tell what was going through my mind." 

Trump has frequently called the border line "imaginary" when musing about annexing Canada.

Canadian history experts say establishing the Canada-U.S. border was, in fact, a long and complex process that involved numerous treaties and took more than a century.

However, they say, Trump does have a point.

"He's just trying to use that to cause chaos and to provoke annoyance to people, and to stir the pot," said Stephen Bown, author of Dominion: The Railway and the Rise of Canada. "But from a historian's point of view, he's not inaccurate, either."

Bown says a lot of international boundary agreements from the 19th century are "somewhat nonsensical" because they were signed by people who didn't know exactly what they were agreeing to.

The drawing of borders between the United States and British North America effectively began in the east with the Treaty of Paris in 1783, following the American Revolution. 

Many treaties followed in the ensuing decades, but it was the Treaty of 1818 that began the long push west, drawing a line across the 49th parallel as British North America and the U.S. expanded — in part because the straight line would be easier to survey than the pre-existing boundaries that were based on watersheds and other natural features.

"When all the lines were just being randomly drawn upon maps by people in conference rooms, often in Europe or in Washington, between various diplomats, none of these people had ever been to any of the land that they were marking up," Bown said. 

"The maps that they were working from were completely inaccurate, because there weren't significant numbers of European-descended settlers living in a lot of that land, especially in the West, during those time periods."

In many cases, the lines bisected through traditional lands of Indigenous Peoples. The Blackfoot Confederacy, for example, stretched through what is now the Canadian Prairies and Montana. 

The Oregon Treaty of 1846 settled a dispute between the British and the Americans, again using the 49th parallel to cut through the Rocky Mountains to the pacific coast, completing the westward push.