In the 1840s, the United States and Mexico fought over?

Mexican-American War, also called Mexican War, Spanish Guerra de 1847 or Guerra de Estados Unidos a Mexico ("War of the United States Against Mexico"), war between the United States and Mexico (April 1846-February 1848) stemming from the United States’ annexation of Texas in 1845 and from a dispute over whether Texas ended at the Nueces River (Mexican claim) or the Rio Grande (U. S. claim). The war-in which U. S. forces were consistently victorious-resulted in the United States’ acquisition of more than 500,000 square miles of Mexican territory extending westward from the Rio Grande to the Pacific Ocean.