Having coined the phrase "manifest destiny" the previous July, journalist John L. O'Sullivan argued in his newspaper New York Morning News that the United States had the right to claim the entire Oregon Country.

Manifest destiny was the imperialist belief in the 19th-century United States that American settlers were destined to expand westward across North America, and that this belief was both obvious ("manifest") and certain ("destiny"). The belief is rooted in American exceptionalism, romantic nationalism, and white nationalism, implying the inevitable spread of republicanism and the American way. It is one of the earliest expressions of American imperialism.

John Louis O'Sullivan was an American columnist, editor, and diplomat who coined the term "manifest destiny" in 1845 to promote the annexation of Texas and the Oregon Country to the United States. O'Sullivan was an influential political writer and advocate for the Democratic Party at that time and served as U.S. minister to Portugal during the administration of President Franklin Pierce (1853–1857).

Oregon Country was a large region of the Pacific Northwest of North America that was subject to a long dispute between the United Kingdom and the United States in the early 19th century. The area, which had been demarcated by the Treaty of 1818, consisted of the land north of 42° N latitude, south of 54°40′ N latitude, and west of the Rocky Mountains down to the Pacific Ocean and east to the Continental Divide. Article III of the 1818 treaty gave joint control to both nations for ten years, allowed land to be claimed, and guaranteed free navigation to all mercantile trade. However, both countries disputed the terms of the international treaty. Oregon Country was the American name, while the British used Columbia District for the region.

December 27 is the 361st day of the year in the Gregorian calendar; four days remain until the end of the year.