James K. Polk was the President of the United States during the Mexican-American War, which took place from 1846 to 1848. Polk was a strong advocate for westward expansion and believed in the concept of Manifest Destiny, which was the idea that it was the United States' destiny to expand its territory across the North American continent. His administration was marked by significant territorial expansion, including the annexation of Texas and the acquisition of the territories that would become California, Arizona, New Mexico, Utah, Nevada, and parts of Colorado and Wyoming as a result of the war with Mexico.
