The 1846 Oregon Treaty established the border between the British and American sections of the Oregon Territory. The Oregon Territory had been jointly occupied by both the British and Americans since 1818 when they established a joint claim over the territory. This arrangement steadily grew intolerable for both sides. American President James Polk ran on the platform "54°40' or fight" in the 1844 election; 54°40' referred to the latitude line that formed the northern border of the Oregon Territory.
The Treaty states that the 49th parallel will form the border of the United States and the British on the mainland. Vancouver Island was an exception that was given to the British in its entirety despite going south of the 49th parallel. The 49th parallel became the US-Canadian border when British Columbia became part of Canada.
