Today, 179 years ago, on August 22, 1846 (July 1, 1846), the United States annexed New Mexico. August 22, 1846 ¨C The United States annexed New Mexico. New Mexico was a state in the southwestern part of the United States, formerly a land of the Mexicans, and after the Mexican War in 1846 became a land of the Americans. In 1912 it was listed as the 42nd state of the United States. The state has many Spanish inhabitants and a few Native Americans. Therefore it has a fairly unique culture. Because of the relationship of the name of the state, it is easy for many Americans to misunderstand that it is the territory of Mexico, it is also the only official state of the United States with two languages, naming the state in Spanish as "Nuevo Mexico", the post office of the state is NM,