The idea of Manifest Destiny arose in response to the prospect of U.S. annexation of Texas and to a dispute with Britain over the Oregon Country, which became part of the union. With its triumph in the Mexican-American War, the United States seemingly realized its Manifest Destiny by gaining an immense domain (more than 525,000 square miles [1,360,000 square km] of land),  including present-day Arizona, California, western Colorado, Nevada, New Mexico, Texas, and Utah.