The war fought between the U.S. and Mexico from 1846 to 1848 is known as the Mexican-American War. The conflict was primarily fueled by territorial disputes following the annexation of Texas by the United States in 1845. The U.S. sought to expand its territory westward, leading to tensions with Mexico, which still considered Texas part of its territory. The war resulted in significant U.S. territorial gains, including California, Nevada, Utah, Arizona, and parts of Colorado and New Mexico, through the Treaty of Guadalupe Hidalgo. This territorial expansion further fueled discussions about slavery and laid the groundwork for future conflicts.