What concept applied in the US during the 1800s justified westward expansion into "unused land"?

Manifest destiny is the concept that emerged in the 19th century in the United States, which held the belief that American settlers were destined to expand across North America. This ideology justified westward expansion into what was considered "unused land," as it framed this movement as a divine right and a duty to spread democracy and civilization. This notion provided a moral and ideological foundation for territorial expansion, suggesting that it was not only acceptable but necessary for the growth and spread of American values.

By asserting that it was the country's destiny to expand, proponents of manifest destiny rationalized the displacement of Native American tribes and the assertion of American sovereignty over vast territories. This concept significantly influenced U.S. policy and attitudes toward expansion during the 1800s, shaping historical narratives and justifying actions that would have far-reaching consequences for indigenous populations.