June 15, 1846 – Oregon Treaty is Signed by the U.S. and Great Britain

The Oregon Treaty, between the United Kingdom and the United States, was signed on this day in history during the presidency of James K. Polk. The treaty brought an end to the Oregon boundary dispute by settling competing American and British claims to the Oregon Country; the area had been jointly occupied by both Britain and the U.S. since the Treaty of 1818.

The Treaty of 1818 had 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. The treaty provided for joint control of that land for ten years. Citizens in both countries could claim land and both countries were guaranteed free navigation throughout.

In 1827 Washington and London agreed to postpone the issue indefinitely subject to one year’s notice by either party. An interim treaty, negotiated by British diplomat Lord Ashburton and Secretary of State Daniel Webster and called the Webster-Ashburton Treaty of 1842, partially delineated the northeastern U.S.-Canada border, but left the border of the Oregon Territory unsettled. Border skirmishes continued, as shared control grew more contentious.

Through tough negotiation and the threat to go to war over the issue, Polk was able to settle on a boundary of 49 degrees north, ceding to Britain what is now British Columbia, but getting for the U.S. all of what is now Washington, Oregon, Idaho, and parts of Montana and Wyoming.

The Senate ratified the treaty by a vote of 41-14 on June 18, 1846. A later controversy over the precise boundaries in the Juan de Fuca Strait was resolved by international arbitration in favor of the United States.

The U.S. portion of the region was organized as Oregon Territory on August 15, 1848, with Washington Territory being formed from it in 1853.