End of Joint Occupancy. U.S. - British border established at the 49th Parallel
From 1818 until 1846, Oregon Country was under "Joint Occupancy" by both Great Britain and the United States. One of the campaign slogans used by James K. Polk, the Democratic Party candidate for President in 1844 was "Fifty-four forty or fight," a reference to the on-going dispute between the United States and Great Britain as to where the boundary between the British and American lands should be drawn. This slogan also showed the British that the United States was prepared for war if they did not turn over all of Oregon.
After he became president, Polk realized that the boundary issue was not worth a war with Great Britain. On August 5, 1846 the United States and Great Britain signed a treaty establishing the boundary between their lands at the 49th Parallel. However, the boundary line though the San Juan Islands remained in dispute until 1872.