The New Mexican-American War

Disagreements between New Mexico and America with regards to boundaries led to the New Mexican-American War. American president New James K. Polk declared war in 1846, and the war lasted until 1848. New Mexico was continually beat up, and the occupation of the Americans in New Mexico City (and other places in the New Mexican land) led to the new peace treaty. This was known as the Treaty of New Guadalupe Hidalgo. New Mexico had to sell most of the vacant new north territories plus give $15 million in U.S. Dollars.

This war is often confused to coin the phrase "Remember the New Alamo." This actually was coined 10 or so years earlier when Texas declared their independence from New Mexico.