Canada–United States border

A line drawn with faulty maps

The border began with the Treaty of Paris in 1783, which ended the Revolutionary War.^[6] It described a line between the new United States and the remaining British colonies from the mouth of the St. Croix River on the Bay of Fundy to the north-westernmost point of the Lake of the Woods, and from there due west to the Mississippi River.^[4]

That description did not fit the real landscape, because the negotiators in 1783 had worked from faulty maps.^[7] The 1794 Jay Treaty already allowed for the chance that a line due west from the Lake of the Woods would never meet the Mississippi.^[4] Later treaties spent decades fixing these gaps. The Jay Treaty also set up commissioners to decide which river was the St. Croix, and the 1814 Treaty of Ghent, which ended the War of 1812, created more commissions to settle islands and stretches of the line.^[4][7]

Those commissions divided the St. Lawrence and the rivers linking the Great Lakes so both countries had navigable channels. They also agreed that present-day Angle Inlet, Minnesota would be the end point of the 1783 line, and that from there the border would run south to the 49th parallel.^[7] That is why the line makes a sharp jog at the Lake of the Woods before it settles on the 49th parallel.^[7][4]

The 49th parallel

The Convention of 1818 ran the border from the Lake of the Woods north or south to the 49th parallel, then west along it to the Rocky Mountains.^[4] West of the Rockies, the Oregon Country was left open to both countries.^[7] The United States wanted to continue the 49th parallel to the Pacific. Britain wanted the line to follow the Columbia River to the ocean instead.^[8]

By 1843 American settlers arriving on the Oregon Trail had made the question urgent, and some in Congress took up the slogan “54 degrees 40 minutes or fight”.^[8] President James Polk proposed the 49th parallel, and Britain agreed, with minor changes that kept all of Vancouver Island on the British side. The US Senate ratified the Oregon Treaty on 18 June 1846.^[8] The line was extended through the Strait of Georgia and Juan de Fuca Strait to the Pacific. A later disagreement over the channel through the islands went to arbitration by the German Emperor, whose award both sides accepted in 1873.^[4]

In the northeast, the commissioners under the Treaty of Ghent had failed to agree on the border next to Maine, and the United States rejected an award by the King of the Netherlands.^[4] When New Brunswick officials arrested Americans in the disputed area, Maine called out its militia.^[6] The Webster–Ashburton Treaty, signed on 9 August 1842, split the disputed land, giving 7,015 square miles to the United States and 5,012 to Britain. It also settled the line through the Great Lakes to the Lake of the Woods.^[6][4]

“Article II of the Convention of 1818 stipulated that the boundary proceed from the north-westernmost point of Lake of the Woods north or south to the 49th parallel and along it to the Stony Mountains (Rockies).”^[4]

Alaska and the 1903 tribunal

The Alaska border is older than the United States' ownership of Alaska. A convention signed by Britain and Russia in February 1825 set the line between Russian America and British territory.^[5] In the north it follows the 141st meridian west. In the south, along the Alaska Panhandle, it was meant to follow the crest of the mountains parallel to the coast, but never more than 10 marine leagues from the ocean.^[5] The United States bought Alaska from Russia in 1867, and with it Russia's side of the 1825 line.^[9][5]

The wording left room for argument about the Panhandle's inlets. The Klondike gold rush of 1898 made it urgent, because Canada wanted a route from the gold fields to the Pacific fjords.^[4][10] A provisional line was set in 1899 across the Chilkoot and White Passes, and a convention of 24 January 1903 created a tribunal of six members: three appointed by Britain and three by the United States.^[4][5]

In the award of 20 October 1903, the tribunal agreed unanimously on where the line started, at Cape Muzon. Its other key answers were decided by four members: the three Americans and Britain's Lord Alverstone.^[5] They found that Russia had been meant to hold a continuous strip of mainland coast, cutting British territory off from the heads of the inlets.^[5] The two Canadian members refused to sign, and the decision set off a strong wave of anti-British feeling in Canada.^[10] Surveyors then marked the Panhandle line and, under a 1906 convention, the 141st meridian, finishing the fieldwork in 1913.^[4]

Keeping the line visible

A treaty of 4 June 1908 created the International Boundary Commission, with one commissioner from each country, to define and mark the whole border accurately.^[11] Until then, many water boundaries had been drawn only as curved lines on charts. The 1908 treaty had them marked with buoys, monuments and ranges.^[4]

A 1925 treaty made the commission permanent and made small changes, including turning the 49th parallel from a slightly curved line between monuments into a series of straight lines.^[11][4] Today the commission keeps a cleared strip 6 m wide along the line through forest and brush, about 2,172 km of it, and maintains thousands of monuments.^[2][3]