"54-40 or Fight" was a campaign slogan used during the 1844 United States Presidential Election by James K. Polk, who would eventually become the 11th President of the United States. The slogan referred to a territorial dispute between the United States and Great Britain over the Oregon Country, which included present-day Oregon, Washington, and parts of Idaho, Montana, and Wyoming.
At the time, the Oregon Country was jointly occupied by the United States and Great Britain, but there was a growing sentiment in the United States that the country should assert its ownership of the region. The slogan "54-40 or Fight" referred to the line of latitude (54° 40') that served as the northern boundary of the disputed territory, and it conveyed the idea that the United States should not settle for anything less than full ownership of the region.
The slogan was important to President Polk and his presidential campaign because it tapped into a sense of American nationalism and expansionism that was prevalent at the time. Polk's campaign promised to aggressively pursue the country's territorial ambitions, and the slogan "54-40 or Fight" became a rallying cry for those who believed in American exceptionalism and manifest destiny.
While the slogan was effective in galvanizing public support, it also increased tensions between the United States and Great Britain, and it raised the risk of war between the two countries. Ultimately, a compromise was reached in 1846, with the United States and Great Britain agreeing to a border at the 49th parallel, which still serves as the border between the United States and Canada today.