I recently received a question from a reader about a piece I wrote on the history of the US – Canada border. I share my reply, below. You may find it useful to pull out a map to follow this.
You had queried why I felt the border between the US and Canada had been ‘settled’ by the end of the War of 1812, given later noises in the 1840s about ‘54-40 or fight’, etc. You are right that it was not all officially settled at the time, but a number of considerations agreed to in the east were simply carried forward westerly.
First of all, the War settled where Great Britain/Canada had control in the East. The St. Lawrence River was split between US and Canadian control going downstream from Lake Ontario, that is, northeast, to near Montreal. There, the border left the River and went due east, giving the mouth of the Ottawa River where it joined the St. Lawrence River just above Montreal to the British/Canadians. This line, in turn, gave the US control over Lake Champlain. The British wanted to keep control over the water routes used in the fur trade and the US wanted to protect New York State from possible future British assaults via Lake Champlain.
The border from there to eastern Maine was left fuzzy for years; the rest of the River and the Gulf of St. Lawrence were clearly British, but where the northern and eastern land borders were, exactly, was not settled until much later. As well, the end of the War of independence in 1783 had left the border undetermined from near Machias, the easternmost Revolutionary fishing village in Maine, north to near the St. Lawrence River. The Americans wanted the eastern border to be along the wide St. John River and the British/Canadians said it had to be west of that river, giving them the only practical inland connection between the Bay of Fundy and Quebec. They had used this route in winter during the War of 1812 to move troops westward.
As the fur trade was still active in the far northwest, this was the big political/economic consideration when it came to the lands west of the St. Lawrence River. Dividing Lakes Huron and Superior the way they did left the St. Lawrence/Ottawa River/Lake Huron/ Lake Superior/Lake of the Woods/ Lake Winnipeg water route still in British/Canadian hands. Since the British still had control over the northern shore of Lake Erie, that Lake was split as well. So, because of where the boundary was, the US had access to all these Lakes. Lake Michigan was completely American, and denied to the Canadians, but it did not lead to the lands where the beaver were.
Before the War of 1812, the US purchase of the Louisiana Territory was interpreted to mean that control of the Missouri River was American wherever the main stream led. The Lewis and Clark exp. in 1806-7 showed that the River did not go as far north as 49 degrees--close (40miles), and that parallel, being the closest, became the border from Lake of the Woods to the Rockies. The border therefore was clear in principle all the way to the Rockies. This was known to both sides before the War of 1812.
Now, we have to go to the Pacific Ocean and look east. The Law of the Sea at the time gave validity of claim to whomever got to a piece of land first and landed on it. An American found the outlet of the Columbia River on a clear day because the British, who had been in the area since Captain Cook, missed it in fogs and storms. Meanwhile, in the 1780s and 90s, British fur traders had penetrated the Vancouver area from inland and from the north, so they were entitled to the Georgia Strait area. The land from Vancouver south to the Columbia River was contested. The US demand for 54 degrees-40minutes north latitude was a negotiating ploy that had as its only basis the fact that there were more American settlerssouthof the Columbia River there were British trappers in what is now British Columbia. If the logic is baffling, well, so be it. The Rocky Mountains area to the coast was divided with an agreement to extend the 49th parallel to the sea, with a squiggle through some islands to give both countries a shared right of passage out to the Pacific, somewhat like the deal made in the Great Lakes.
The War of 1812 settled it, for all intents and purposes, no matter when various treaties got signed.