GADSDEN PURCHASE

(signed Dec. 30, 1853, Mexico City; revised treaty ratified April 25, 1854), transaction that followed the conquest of much of northern Mexico by the United States in 1848. It assigned to the United States nearly 30,000 additional square miles (78,000 square kilometres) of northern Mexican territory, now southern Arizona and southern New Mexico. Prompted by advocates of a southern transcontinental railroad for which the most practical route would pass through the acquired territory, and by demands for U.S. protection of private concessions in the area, the purchase was negotiated by the U.S. minister to Mexico, James Gadsden, for $10,000,000.