The phrase "54 40 or Fight" was a slogan created by Democratic nominee James K. Polk in an attempt to rally the public in support of removing control of portions of the United States, including Texas, California and Oregon, from the British. Geographically, the 54 40 line refers to the northern borderline of Oregon, which then formed the northernmost limit of the territory the U.S. sought to acquire from Britain. The idea behind acquiring additional land from British control derived from the concept of manifest destiny, which played a crucial role in shaping the domestic policies of the U.S.
At the time Polk ran as candidate for U.S. president, the Oregon Territory was one of two land areas with disputed ownership. In addition to the Oregon Territory, which included the modern states of Oregon, Idaho, Washington, Alaska and parts of the western Canadian coast, the U.S. and Great Britain claimed rightful ownership to the southwestern part of the U.S. that shared a border with Mexico. In the Treaty of 1818, the U.S. and Britain agreed to a joint ownership of the disputed regions but, in 1846, the two nations divided the Oregon Territory at the 49th parallel. Each nation claimed ownership of half.