The United States and Great Britain signed the Treaty of Oregon on June 15, 1846, ending 28 years
of joint occupancy of the Pacific Northwest. The treaty established the 49th
parallel as the border between the two countries. The United States and Great
Britain ended the War of 1812 with the Treaty of Ghent in 1814, and four years
later agreed to a 10-year period of joint occupancy of the Northwest.
The joint-occupancy agreement was renewed twice, but by 1846 it was clear that the
Northwest was rapidly becoming American, primarily as the result of westward
migration on the Oregon Trail, and neither country wanted to fight
another war over the border issue. Some members of Congress wanted the northern
United States border established at the southern extent of Russian Alaska, at
54 degrees 40 minutes north latitude. Britain would have preferred the Columbia
River as the boundary but was willing to consider a border farther north — but
not 54 degrees north — and President James Polk, facing war with Mexico, was
willing to compromise in order to resolve the issue.
The result of negotiations was a border at 49 degrees north, which gave the British
possession of Vancouver Island, an important acquisition for Britain and a
concession for the United States. On August 14, 1848, Congress formally
established the Oregon Territory, which embraced the present-day states of
Washington, Oregon, and Idaho.