Final answer:
The Oregon Country tensions were resolved by the Oregon Treaty of June 1846, establishing the 49th parallel as the boundary between U.S. and British territories. This followed President Polk's initial demand to extend American control up to the latitude of 54° 40' but concluded with a more pragmatic compromise.
Step-by-step explanation:
The Oregon Country tensions involved a dispute between the United States and Great Britain over the region known as Oregon Country, which included present-day Oregon, Washington, Idaho, and parts of British Columbia. President James K. Polk, whose campaign slogan in 1844 was "Fifty-four forty or fight!", advocated for the United States' claim to the entire region up to the latitude of 54° 40'. This assertion was based on the idea of Manifest Destiny and a desire to expand American territory westward. The 54° 40' line represented the northern border of Oregon Country, as claimed by expansionists. Although Polk was prepared to fight for this territory, he was also open to compromise and eventually agreed to establish the boundary at the 49th parallel after realizing Britain's position was quite strong. The dispute was peacefully resolved through negotiations, leading to the signing of the Oregon Treaty in June 1846, which formalized the 49th parallel as the boundary between U.S. and British territories in the Pacific Northwest. This compromise provided the United States with a valuable Pacific port in Puget Sound and balanced the addition of new territories between free and slave states.