The Mexican-American War, conducted between the United States and Mexico from 1846 to 1848, served to fulfill America's "manifest destiny" to expand its territory across the entire North American continent. And marked the first US conflict fought in foreign soil.
A border encounter along the Rio Grande ignited off the fighting and was succeeded by a series of U.S. victories. Mexico had lost about one-third of its territory, including nearly all of present-day California, Utah, Nevada, Arizona, and New Mexico.