The Treaty of 1818 set the boundary between the United States and British North America along the 49th parallel of north latitude from Minnesota to the "Stony Mountains" (now known as the Rocky Mountains). The region west of those mountains was known to the Americans as the Oregon Country and to the British as the Columbia Department or Columbia District of the Hudson's Bay Company. (Also included in the region was the southern portion of another fur district, New Caledonia.) The treaty provided for joint control of that land for ten years. Both countries could claim land and both were guaranteed free navigation throughout.
Original manuscript of the treaty (transcription
), as kept by the U.S. National Archives.
Joint control steadily grew less tolerable for both sides. After a British minister rejected U.S. President James K. Polk's offer to settle the boundary at the 49th parallel north, Democratic expansionists called for the annexation of the entire region up to Parallel 54°40′ north, the southern limit of Russian America as established by parallel treaties between the Russian Empire and the United States (1824) and Britain (1825). However, after the outbreak of the Mexican–American War in April 1846 diverted U.S. attention and military resources, a compromise was reached in the ongoing negotiations in Washington, D.C., and the matter was settled by the Polk administration (to the dismay of its own party's hardliners) to avoid a two-war situation and a third war with the formidable military strength of Great Britain in less than 70 years.