On June 15, 1846, Britain and the United States signed the Oregon Treaty, which defined the 49th parallel as the primary international border in the Pacific Northwest. Since 1818, the entire region, including present-day Washington, Oregon and Idaho, as well as much of British Columbia, has been in shared occupation, where citizens of both countries travel freely and trade. In 1845, the Americans adopted the phrase “Fifty Four Forty or Fight!” and referred to the 54-degree, 40-minute latitude line, a more northern border that would give the United States much of what Canada is today. However, the United States is not prepared to actually wage war on this issue because it is at war with Mexico on the southern border. So the United States and the United Kingdom reconciled by extending the 49th parallel border — which has long been established east of the Rockies — to the Pacific. With the sole exception of the 49-degree line, both sides agreed to swing the border around Vancouver Island to the south, which Britain gives To Vancouver Island. The continental border between the United States and Canada will remain unchanged from that date on. Intercity american migration to Oregon began in the early 1840s. In 1840, about 150 Americans lived in the Oregon Country. Until 1845, there were 5,000 or more American settlers, most of them clustered in the Valley of La Willamette (see figure below).
Most of them had arrived via the road and thus launched an epic new means of transport. The sudden growth of a resident American population and settlers, not fur traders, changed the balance of power in the region that would become American territory. Map of Oregon Territory showing what the United States claimed and what the United States and the British claimed in 1845-46 The treaty also had the unintended consequence that what Point Roberts, Washington, became on the “wrong” side of the border. A peninsula in southern Canada in Boundary Bay was manufactured by the accord as a country south of the 49th parallel, a distinct fragment of the United States.
