The significance of the signing of the Treaty of Guadalupe Hidalgo in 1848 was profound, as it ended the Mexican-American War and resulted in the U.S. acquiring vast territories, including what is now California, Arizona, New Mexico, Nevada, Utah, and portions of Colorado and Wyoming. This significantly expanded U.S. landholdings and fueled further westward expansion. The treaty also established the Rio Grande as the border between Texas and Mexico. While it resolved the war, it deepened sectional tensions over slavery in new territories, contributing to the divisive atmosphere leading up to the American Civil War.