Oregon Treaty sets the 49th parallel boundary

Background. The Oregon boundary dispute involved competing territorial claims in the Pacific Northwest. In 1844, the Democratic Party proposed annexing the entire area, while British negotiator Earl of Aberdeen initially accepted the 49th parallel if Vancouver Island remained British. President Polk asserted U.S. title was clear, but diplomatic channels continued throughout 1845, with Everett supporting a revision to allow Britain to keep Vancouver Island.

Negotiation. Tensions peaked in 1845 and 1846, with Polk recommending notice to terminate joint occupation. The outbreak of the Mexican-American War in April 1846 diverted U.S. attention, leading to a compromise in Washington, D.C. to avoid a two-war situation. The British offered to negotiate boundaries west of the Rockies in early June 1846, resulting in the formal treaty drawn up by Pakenham and Buchanan.

Terms. The treaty established the border along the 49th parallel until the Strait of Georgia, where the marine boundary curved south to exclude Vancouver Island and the Gulf Islands from the United States. This arrangement made Oregonians south of the parallel American citizens and those north of it British. The agreement was ratified by the U.S. Senate on June 18, 1846, by a vote of 41–14.