This phrase, popularized by journalist John O'Sullivan in the 1840s, articulated the belief that the United States was destined to expand its territory across North America, from the Atlantic to the Pacific Ocean. It justified westward expansion and the acquisition of new territories like Texas, California, and the Mexican Cession.
While the term "Manifest Destiny" wasn't coined by John O'Sullivan, he was a key figure in popularizing the idea and making it a central element of American national identity.