The Gadsden Purchase, completed in 1854, involved the acquisition of land from Mexico, specifically parts of present-day southern Arizona and New Mexico. The United States negotiated a purchase of approximately 29,670 square miles for $10 million with the intention of facilitating a southern route for a transcontinental railroad. This acquisition was significant not only for its economic implications but also for enhancing U.S. territorial expansion and solidifying boundaries following the Mexican-American War. It also contributed to ongoing tensions regarding slavery in newly acquired territories, which would later play a role in the events leading up to the Civil War.