The Mexican–American War was an armed conflict between the United States and Mexico from 1846 to 1848 in the wake of the 1845 U.S. annexation of Texas. Mexico claimed ownership of Texas as a breakaway province and refused to recognize the secession and subsequent military victory by Texas in 1836.
In the U.S. the conflict is often referred to simply as the Mexican War and infrequently as the U.S.–Mexican War. In Mexico, terms for it include Intervención Estadounidense en México (American intervention in Mexico), Invasión Estadounidense de México (American[a] Invasion of Mexico), and Guerra del 47 (The War of '47).
The most important consequences of the war for the United States were the Mexican terms of surrender under the Treaty of Guadalupe Hidalgo, in which the Mexican territories of Alta California and Santa Fe de Nuevo México were ceded to the United States. In Mexico, the enormous loss of territory following the war encouraged its government to enact policies to colonize its remaining northern territories as a hedge against further losses. In addition the Rio Grande became the boundary between Texas and Mexico, and Mexico never again claimed ownership of Texas.