The expansionist ideology that drove U.S. policy during the late 19th century is known as Manifest Destiny. This belief held that the United States was destined to expand across the North American continent, spreading its values and institutions. Manifest Destiny justified the annexation of territories, including Texas and parts of California, often at the expense of Native American lands and other nations. It also fueled imperialistic ambitions, leading to involvement in conflicts such as the Spanish-American War, which resulted in U.S. territorial acquisitions in the Caribbean and the Pacific, further cementing America’s role as an emerging global power.