Manifest Destiny, in United States history, a slogan expressing the spirit of national expansion in the period after 1845. The phrase first referred to the inevitability of expansion to the Pacific. After the Texas annexation, the Mexican War cession, and the Oregon settlement, some nationalists spoke of a destiny that included all North America. This spirit led to the purchase of Alaska in 1867, and about 1900 it resulted in the acquisition of overseas territories, such as Hawaii and Puerto Rico.