The Canada-US border is one of the most peaceful international borders in the world today, and in fact it is the longest un-militarized border in the world. Despite this, it has actually been the subject of quite a few controversies over the past few hundred years.
The location of the present Canada-US border was set by the Treaty of Paris in 1783, which ended the Revolutionary War. The Jay Treaty of 1794 created the International Boundary Commission, whose responsibility it was to survey and later to map this boundary. Their task was made difficult by the terrain, which includes mountains, heavy forests, remote farmlands, the Great Lakes and other bodies of water.
After the Louisiana Purchase of 1803, in which the United States gained a large swath of western land, it was generally agreed that the boundary between this land and Canada was along the watershed between the Missouri and Mississippi rivers on one side and the Hudson Bay basin on the other. Since it is very difficult to survey a watershed-based boundary in an area of level plains, a compromise in 1818 set the boundary at the 49th parallel, extending west to the Rocky Mountains. Because this line was originally surveyed using nineteenth-century techniques, in some places the boundary line differs from the actual 49th parallel by as much as several hundred feet.
As civilization expanded westward, the US-Canada boundary was later extended along the 49th parallel. Disputes along this boundary resulted in a little-known war in America’s history called the Aroostook War. The resulting Webster-Ashburton Treaty of 1842 better defined the boundary, particularly between Maine in the United States and New Brunswick in Canada, as well as between present-day Ontario and Minnesota in the Great Lakes region.
Just two years later, in 1844, another dispute arose about the boundary line near the western coast. The Oregon Treaty resolved this conflict in 1846, establishing the 49th parallel as the boundary line all the way to the Pacific Ocean. Above present-day Washington State, the boundary with British Columbia was set in the middle of the Strait of Juan de Fuca. The Northwest Boundary Survey (1857-1861) laid out this boundary on the land, but not over the water. There are actually two straits in the Strait of Juan de Fuca that could be considered the middle of the channel, making the surveyors’ task difficult there.
The water boundary between present-day Washington State and British Columbia was not actually settled until after the 1859 Pig War, so named because the war started when a farmer shot a pig on his land. After years of tension, this boundary was finally settled in 1872 by a third-party commission.
In 1925, the International Boundary Commission which had first been established in 1794 was finally made a permanent organization. A joint commission with both American and Canadian members, it is responsible today for surveying and mapping the boundary between the US and Canada, and for maintaining permanent boundary monuments on land and boundary buoys in water. This commission operates on an annual budget of about $1.4 million USD.