Manifest Destiny was a widely held belief in the 19th-century United States that American settlers were destined—by God or by a sense of mission—to expand their territory across the entire North American continent, from the Atlantic Ocean to the Pacific Ocean. This ideology was used to justify the westward expansion of the U.S., including the annexation of territories and displacement of Native American tribes.

The concept emerged in the 1840s and was a driving force behind events like the Texas Annexation, the Oregon Trail migrations, and the Mexican-American War. Proponents of Manifest Destiny believed that expansion was not only good but also obvious (“manifest”) and certain (“destiny”). This belief had significant impacts on U.S. policy and contributed to conflicts both within the country and with neighboring nations.