in U.S. history, the supposed inevitability of the continued territorial expansion of U.S. boundaries westward to the Pacific, and even beyond. The idea of “Manifest Destiny” was often used by American expansionists to justify U.S. annexation of Texas, Oregon, New Mexico, and California and later U.S. involvement in Alaska, Hawaii, and the Philippines.

John L. O'Sullivan coined the phrase in his United States Magazine and Democratic Review (July–August 1845) to prophesy “the fulfillment of our manifest destiny to overspread the continent allotted by Providence. . . .” Congressmen quickly adopted the term in their debates over the three territorial questions confronting the United States in 1845 and 1846—the annexation of Texas, the joint occupation of the Oregon Territory with England, and the prosecution of war with Mexico. Although chiefly a tenet of the Democrats, individual Whigs or Republicans also supported Manifest Destiny, which in the 1890s was revived as a Republican policy.