The Gadsden Purchase (Spanish: Venta de La Mesilla, lit. 'La Mesilla sale'), also known as the Treaty of Mesilla, is the acquisition of a 29,640-square-mile (76,800 km2) region of present-day southern Arizona and southwestern New Mexico by the United States from Mexico. The first draft was signed on December 31, 1853, by James Gadsden, US Minister to Mexico, and by Antonio López de Santa Anna, president of Mexico. The treaty took effect on June 8, 1854.
The purchase included lands south of the Gila River and west of the Rio Grande, where the United States wanted to build what is now known as the Sunset Route, a transcontinental railroad to California which the Southern Pacific Railroad later completed in 1881–1883. These lands allowed the railroad to follow a flatter and more direct route, lowering its anticipated costs and allowing faster completion, and particularly encouraging a route to a port in the Southern United States on the Gulf of Mexico. The purchase also clearly defined the current Mexico–United States border.
The Santa Anna government, in financial distress, accepted the sale, which brought Mexico US$10 million (equivalent to $358.3 million in 2025). Following the devastating loss of Mexican territory to the U.S. in the Mexican–American War (1846–48) and the ongoing unauthorized military expeditions in the region led by the territorial governor of New Mexico and known filibuster William Carr Lane, some historians argue that Santa Anna may have calculated that it was better to cede territory through a treaty and receive payment rather than risking the United States simply seizing the territory.
The Gadsden Purchase was the last substantial territorial enlargement of the contiguous United States. The Arizona cities of Yuma, Tucson, Nogales, Sierra Vista, Tombstone, and Douglas, as well as the New Mexico city of Deming are on territory acquired by the U.S. in the Gadsden Purchase.
Desire for a southern transcontinental rail line
As the railroad age evolved, business-oriented Southerners saw that a railroad linking the South with the Pacific Coast in California would expand trade opportunities. They thought the topography of the southern portion of the original Mexican Cession was too mountainous to allow a direct route. Projected southern railroad routes tended to veer to the north as they proceeded eastward, which would favor connections with northern railroads and ultimately favor northern seaports. Southerners saw that to avoid the mountains, a route with a southeastern terminus might need to swing south into what was still Mexican territory.
The administration of President Pierce, strongly influenced by Secretary of War Jefferson Davis, a Southerner from Mississippi, saw an opportunity to acquire land for the railroad, as well as to acquire significant other territory from northern Mexico. In those years, the debate over slavery in the United States affected many issues, as the acquisition of new territory opened the question of whether it would be slave or free territory. In this case, the debate over slavery ended progress on construction of a southern transcontinental rail line until the early 1880s, although the preferred land became part of the nation and was used as intended after the Civil War.
Southern route for the transcontinental railroad
Southern commercial conventions
In January 1845, Asa Whitney of New York presented the United States Congress with the first plan to construct a transcontinental railroad. Although Congress took no action on his proposal, a commercial convention in Memphis later that year took up the issue. Prominent attendees included John C. Calhoun, Clement C. Clay Sr., John Bell, William Gwin, and Edmund P. Gaines, but James Gadsden of South Carolina was influential in the convention's recommending a southern route for the proposed railroad. The route was to begin in Texas and end in San Diego or Mazatlán. Southerners hoped that such a route would ensure Southern prosperity, while opening the "West to southern influence and settlement".
Southern interest in railroads in general, and the Pacific railroad in particular, accelerated after the conclusion of the Mexican–American War in 1848. During that war, topographical officers William H. Emory and James W. Abert had conducted surveys that demonstrated the feasibility of a railroad's originating in El Paso or western Arkansas and ending in San Diego. J. D. B. DeBow, the editor of DeBow's Review, and Gadsden both publicized within the South the benefits of building this railroad.
Gadsden had become the president of the South Carolina Canal and Rail Road Company in 1839; about a decade later, the company had laid 136 miles (219 km) of track extending west from Charleston, South Carolina, and was $3 million (equivalent to $90 million in 2025) in debt. Gadsden wanted to connect all Southern railroads into one sectional network. He was concerned that the increasing railroad construction in the North was shifting trade in lumber, farm and manufacturing goods from the traditional north–south route based on the Ohio and Mississippi rivers to an east–west axis that would bypass the South. He also saw Charleston, his home town, losing its prominence as a seaport. In addition, many Southern business interests feared that a northern transcontinental route would exclude the South from trade with the Orient. Other Southerners argued for diversification from a plantation economy to keep the South independent of northern bankers.
In October 1849, the southern interests held a convention in Memphis, in response to a convention in St. Louis earlier that fall which discussed a northern route. The Memphis convention overwhelmingly advocated the construction of a route beginning there, to connect with an El Paso, Texas to San Diego, California line. Disagreement arose only over the issue of financing. The convention president, Matthew Fontaine Maury of Virginia, preferred strict private financing, whereas John Bell and others thought that federal land grants to railroad developers would be necessary.
James Gadsden and California
Gadsden supported nullification in 1831. When California was admitted to the Union as a free state in 1850, he advocated secession by South Carolina. Gadsden considered slavery "a social blessing" and abolitionists "the greatest curse of the nation".
When the secession proposal failed, Gadsden worked with his cousin Isaac Edward Holmes, a lawyer in San Francisco since 1851, and California state senator Thomas Jefferson Green, in an attempt to divide California into northern and southern portions and proposed that the southern part allow slavery. Gadsden planned to establish a slave-holding outpost there based on rice, cotton, and sugar, and wanted to use slave labor to build a railroad and highway that originated in either San Antonio or the Red River valley. The railway or highway would transport people to the California gold fields. Toward this end, on December 31, 1851, Gadsden asked Green to secure from the California state legislature a large land grant located between the 34th and 36th parallels, along the proposed dividing line for the two California states.
A few months later, Gadsden and 1,200 potential settlers from South Carolina and Florida submitted a petition to the California legislature for permanent citizenship and permission to establish a rural district that would be farmed by "not less than Two Thousand of their African Domestics". The petition stimulated some debate, but it finally died in committee.
Stephen Douglas and land grants
The Compromise of 1850, which created the Utah Territory and the New Mexico Territory, would facilitate a southern route to the West Coast since all territory for the railroad was now organized and would allow for federal land grants as a financing measure. Competing northern or central routes championed, respectively, by U.S. Senators Stephen Douglas of Illinois and Thomas Hart Benton of Missouri, would still need to go through unorganized territories. Millard Fillmore established a precedent for using federal land grants when he signed a bill promoted by Douglas that allowed a south to north, Mobile to Chicago railroad to be financed by "federal land grants for the specific purpose of railroad construction". To satisfy Southern opposition to the general principle of federally supported internal improvements, the land grants would first be transferred to the appropriate state or territorial government, which would oversee the final transfer to private developers.
By 1850, however, the majority of the South was not interested in exploiting its advantages in developing a transcontinental railroad or railroads in general. Businessmen like Gadsden, who advocated economic diversification, were in the minority. The Southern economy was based on cotton exports, and then-current transportation networks met the plantation system's needs. There was little home market for an intra-South trade. In the short term, the best use for capital was to invest it in more slaves and land rather than in taxing it to support canals, railroads, roads, or in dredging rivers. Historian Jere W. Roberson wrote:
Southerners might have gained a great deal under the 1850 land grant act had they concentrated their efforts. But continued opposition to Federal aid, filibustering, an unenthusiastic President, the spirit of "Young America", and efforts to build railroads and canals across Central America and the Isthmus of Tehuantepec in Mexico divided their forces, leaving a lot of time for the Pacific railroad. Moreover, the Compromise of 1850 encouraged Southerners not to antagonize opponents by resurrecting the railroad controversy.
— Jere W. Roberson, "The South and the Pacific Railroad, 1845–1855" (April 1974)
Treaty of Guadalupe Hidalgo
The Treaty of Guadalupe Hidalgo (1848) ended the Mexican–American War, but left issues affecting both sides that still needed to be resolved: possession of the Mesilla Valley, protection for Mexico from Indian raids, and the right of transit in the Isthmus of Tehuantepec.
Mesilla Valley
The treaty provided for a joint commission, made up of a surveyor and commissioner from each country, to determine the final boundary between the United States and Mexico. The treaty specified that the boundary, after following the Rio Grande River from the sea, would turn west from the river eight miles (13 km) north of El Paso. The treaty was based on an 1847 copy (the Disturnell Map) of a twenty-five-year-old map which was incorporated into the treaty. However, surveys revealed that El Paso was 36 miles (58 km) further south and 100 miles (160 km) further west than the map showed. Mexico favored the map, but the United States put faith in the results of the survey. The disputed territory involved a few thousand square miles and about 3,000 residents; more significantly, it included the Mesilla Valley. Bordering the Rio Grande River, the valley consisted of flat desert land measuring about 50 miles (80 km), north to south, by 200 miles (320 km), east to west. This valley was thought to be essential for construction of a transcontinental railroad using a southern route.
John Bartlett of Rhode Island, the United States negotiator, agreed to allow Mexico to retain the Mesilla Valley by setting the point at which the boundary commenced toward the west from the Rio Grande River at 32° 22′ N. This point was north of the American claim of 31° 52′ N and, at the easternmost part, also north of the Mexican-claimed boundary at 32° 15′ N, both also on the Rio Grande River). Bartlett's agreement to 32° 22′ N was in exchange for a boundary westward from the river that did not turn north until 110° W in order to include the Santa Rita del Cobre Mountains (sometimes referred to simply as the Cobre Mountains) located in current New Mexico east of current-day Silver City. This area was believed to have rich copper deposits, and some silver and gold which had not yet been mined. Southerners opposed retention of the Mesilla Valley by Mexico because of its implication for the railroad, but President Fillmore supported it. Southerners in Congress prevented any action on the approval of this separate border treaty and eliminated further funding to survey the disputed borderland. Robert B. Campbell, a pro-railroad politician from Alabama, later replaced Bartlett. Mexico asserted that the commissioners' determinations were valid and prepared to send in troops to enforce the unratified agreement.
Native American raids
Article XI of the Treaty of Guadalupe Hidalgo contained a guarantee that the United States would protect Mexicans by preventing cross-border raids by local Comanche and Apache tribes. At the time the treaty was ratified, Secretary of State James Buchanan had believed that the United States had both the commitment and resources to enforce this promise. Historian Richard Kluger, however, described the difficulties of the task:
Comanche, Apache, and other tribal warriors had been punishing Spanish, Mexican, and American intruders into their stark homeland for three centuries and been given no incentive to let up their murderous marauding and pillaging, horse stealing in particular. The U. S. Army had posted nearly 8,000 of its total of 11,000 soldiers along the southwestern boundary, but they could not halt the 75,000 or so native nomads in the region from attacking swiftly and taking refuge among the hills, buttes, and arroyos in a landscape where one's enemies could be spotted twenty or thirty miles away.