The Gadsden Purchase, ratified by president Franklin Pierce on June 24, 1853, added nearly 30,000 square miles to American territory in the desert southwest. The United States government paid ten million dollars to Mexico for the land that was originally bought in hopes of extending a southern route to a proposed transcontinental railroad. The purchase was originally envisioned to include a much larger chunk of Mexico, but was widely opposed by the Mexican people and by abolitionist politicians – who saw the purchase as an attempt to acquire more slave territory.
The Gadsden Purchase, which encompassed southern portions of modern-day Arizona and New Mexico, was organized into the New Mexico Territory upon its purchase. During the Civil War, the Union and Confederacy divided the territory into the Confederate Territory of Arizona and the Territory of Arizona (Union land which included the part of the Gadsden Purchase which is now New Mexico).