Mexican–American War: Mexico ratifies the Treaty of Guadalupe Hidalgo, thus ending the war and ceding California, Nevada, Utah and parts of four other modern-day U.S. states to the United States for US$15 million.

The Mexican–American War, also known in the United States as the Mexican War and in Mexico as the United States intervention in Mexico, was an invasion of Mexico by the United States. It followed the 1845 American annexation of Texas, which Mexico still considered its territory because it refused to recognize the Treaties of Velasco, signed by President Antonio López de Santa Anna after he was captured by the Texian Army during the 1836 Texas Revolution. The Republic of Texas was de facto an independent country, but most of its Anglo-American citizens who had moved from the United States to Texas after 1822 wanted to be annexed by the United States.