Mexican-American War: A war fought between the United States and Mexico from 1846 to 1848, which resulted in significant territorial gains for the U.S., including California and New Mexico.
Manifest Destiny: The belief that it was America's destiny to expand westward across North America, driving territorial expansion.
Treaty of Guadalupe Hidalgo: The treaty signed in 1848 that ended the Mexican-American War and established the Rio Grande as the border between Texas and Mexico. It also ceded large portions of land from Mexico to the United States, including California and New Mexico.