New Mexico was colonized by Spain throughout the 1500s, but the U.S. acquired most of the state in 1848 with the rest becoming a U.S. Territory in 1854 under the Gadsden Purchase, a treaty that turned over southwestern New Mexico and southern Arizona to the U.S. from Mexico,
New Mexicans aided the Union during the Civil War, helping to stop a Confederate invasion. Confederates had occupied Santa Fe in 1862. Volunteers from New Mexico and Colorado joined Union soldiers to defeat Confederate Gen. Henry Hopkins' army in a battle that has been called the Gettysburg of the West.
A reputation for lawlessness developed in New Mexico because of the Lincoln County War, a range war between merchants and cattlemen from 1878 to 1881, and the emergence of outlaws such as William H. Bonney, known as Billy the Kid.
Territorial disputes were resolved and economic progress took place with the arrival of the Atchison, Topeka and Santa Fe Railroad, which crossed through New Mexico beginning in 1879.
Volunteers from New Mexico once again came to the aid of the U.S. by enlisting in Theodore Roosevelt's Rough Riders to fight in the Spanish-American War in 1898. Roosevelt was impressed with the volunteers and worked to bring statehood to New Mexico, which finally became a state in 1912 under President William H. Taft.
