The Gadsden Purchase resulted from the 1853 negotiations between the United States and Mexico for the purchase of the Mesilla Valley, south of the Territory of New Mexico (which included Arizona at the time). By the terms of the treaty, the United States acquired 29,670 square miles south of the Gila River for which the United States paid Mexico $10 million. Mexico had already ceded some two hundred thousand square miles of its northwestern lands, including what would become the present-day states of California, Arizona, New Mexico, Nevada, and Utah. Also, Mexico had accepted a newly redrawn border between itself and the United States, according to the terms of the Treaty of Guadalupe Hidalgo, which brought an end to the Mexican-American War in 1848.
A combination of factors led to the Gadsden Purchase. At the war's end, gold was discovered in California, bringing tens of thousands of people across the North American continent, or by sea around Cape Horn, or across the Isthmus of Panama. California joined the Union on September 9, 1850, and the new state's residents clamored for a more efficient means of transportation and communication with the East. Railroads were already displacing canals as interstate arteries east of the Mississippi River, and several proposals were being introduced in Congress for the construction of a transcontinental railroad.
James Gadsden (1788–1858), president of the South Carolina Railroad Company since 1839, had early recognized the possibility of a transcontinental railroad heading west from El Paso, Texas, through New Mexico and Arizona, to California. Such a route would avoid the obstacles of the Rocky Mountains and the Sierra Nevada range. Gadsden believed that the southern railroads could be consolidated into a single system that would connect California to the South. As early as 1851, Gadsden supported breaking up California into two states, with the southern half utilizing slave labor to cultivate rice, cotton, and sugar. This proposal went nowhere, although the idea of making California into two states was under consideration in Congress when the Civil War began.
Land surveys after the Mexican-American War showed that a railroad route across central New Mexico and Arizona was not geographically feasible. A more viable route lay further south, but it went through the Mesilla Valley, which was still part of Mexico following the war. With Californians demanding a rail connection to the East, and knowing the Mexican government was bankrupt, Gadsden saw an opportunity to make a southern rail route a reality. Secretary of War Jefferson Davis, a fellow southerner and railroad supporter, persuaded President Franklin Pierce to appoint Gadsden as U.S. minister to Mexico, empowering him to negotiate the purchase of the Mesilla Valley.
Antonio Lopez de Santa Anna, president of Mexico, was amenable to discussing the sale of the Mesilla Valley. The Mexican treasury was empty and the government badly in need of funds. Initially, Gadsden pushed for the inclusion of Baja California in the land deal, offering a grand total of $15 million, but the U.S. Senate balked at the cost, cutting out Baja California and reducing the offer to $10 million. In setting the southern border of the purchased area as a straight line to the point where California's southern border met the Colorado River, the treaty left the river as an international waterway. This was a political headache until a treaty conceded water rights to Mexico in 1944.
The negotiators reached agreement in Mexico City on December 30, 1853; the U.S. Senate ratified the treaty on April 25, 1854; and Santa Anna signed the treaty on June 8, 1854. The purchase proved unpopular in both nations. Mexico had lost some 40 percent of its national territory in the recent war, and President Santa Anna had agreed to sell another chunk of Mexican land. This action provoked the Mexican people to revolt; Santa Anna lost the presidency and went into exile, his quarter-century of practicing power politics at an end.
Although the U.S. Senate had approved the Gadsden Purchase, the deal ran afoul of the sectional rivalry between North and South. Antislavery senators objected to the proslavery bias of the purchase. A month before President Pierce approved the Gadsden Purchase, he had signed the Kansas-Nebraska Act, endorsing possible railroad routes from the Midwest to the Pacific and making Chicago, Illinois, the city that would tie the railroad economically to the East. When the Civil War began, the departure of southerners from Congress made it easy for President Abraham Lincoln to approve a bill for a Pacific railroad through Nebraska and across Utah and Nevada to California. Gadsden, who died in 1858, never saw the realization of his vision, for the railroad route through the Mesilla Valley was not completed until well after the Civil War.
See also Arizona; Guadalupe Hidalgo, Treaty of (1848)