Manifest Destiny: The belief in the 19th century that it was America's destiny to expand its territory from coast to coast.
Mexican Cession: Refers to the land Mexico had to give up after losing the Mexican-American War, including present-day California, Nevada, Utah, Arizona, and parts of New Mexico, Colorado, Wyoming, and Texas.
Oregon Territory: A region in the Pacific Northwest that was jointly occupied by Great Britain and the United States until a treaty divided it along the 49th parallel in 1846.