The slogan refers to a dispute between the United States and Great Britain over Oregon Country, which an 1818 treaty allowed both nations to occupy. This was the territory that began at 42 degrees north latitude (the southern boundary of present-day Oregon) and extended north to 54 degrees 40 minutes north latitude (in present-day British Columbia). During the 1830s and early 1840s American expansionists insisted that U.S. rights to the Oregon Country extended north to latitude 54 degrees 40 minutes, which was then the recognized southern boundary of Russian America (roughly present-day Alaska).

The eleventh president of the United States, James K. Polk (1795–1849), used the slogan in his political campaign of 1844. After he was elected, Polk settled the dispute with Great Britain (in 1846), and the boundary was set at 49 degrees north, the northern boundary of what is today Washington State and the border between the United States and Canada. This agreement—reached without the fight threatened in the slogan—gave the United States the territory lying between 42 and 49 degrees north latitude and Great Britain the territory between 49 degrees and 54 degrees 40 minutes north latitude as well as Vancouver Island. The United States’ portion is present-day Washington, Oregon, and Idaho as well as parts of Montana and Wyoming.