Northwest Boundary Dispute, in United States history, a controversy over the possession of the Pacific Northwest. In the early 1800's the United States, Great Britain, Russia, and Spain all claimed the area. However, in 1819 Spain gave up its claims north of 42°north latitude, and in 1825 Russia gave up its claims south of 54°40'. Meanwhile, in the Convention of 1818, Britain and the United States had agreed to make 49° north latitude the northern boundary of the United States from the Lake of the Woods to the Continental Divide. The Pacific Northwest, pending a boundary settlement, was opened to citizens of both countries.
Immigration into the area strengthened the bargaining position of the United States, and President James K. Polk pressed for a settlement after taking office in 1845. The real dispute narrowed down to what is now the western half of the state of Washington. On June 15, 1846, the Oregon Treaty was signed, extending the boundary of the 49th parallel to Puget Sound, the Democratic slogan of "54–40 or fight" having been conveniently forgotten. Britain received Vancouver Island. Because of vague wording in the treaty, a dispute continued over the San Juan Islands, at the northern end of Puget Sound. The islands came under joint British-United States control in 1859 and were awarded to the United States by arbitration in 1872.
