16. The Gadsden Purchase
In 1853, the United States acquired a strip of land from Mexico known as the Gadsden Purchase, aimed at facilitating a southern transcontinental railroad. This area, now part of southern Arizona and New Mexico, remains within U.S. borders today. The purchase highlights the fluidity of territorial boundaries in the American Southwest and the ambitions driving westward expansion. Explore the original treaty at the U.S. National Archives.
