Map Depicting the Gadsden Purchase
These continuing tensions between Mexico and the United States complicated U.S. efforts to find a southern route for a transcontinental railroad as the only viable routes passed through Mexican territory. In 1847, the United States attempted to buy the Isthmus of Tehuantepec, an isthmus on the southern edge of North America, as an alternative means of providing a southern connection between the Atlantic and Pacific oceans. Mexico, however, had already granted Mexican Don José de Garay the right to build colonies for Americans on the isthmus with capital from the New Orleans Company. Fearing the colonists would rebel as those in Texas had, Mexican President Juan Ceballos revoked the grant, angering U.S. investors.
In 1853, Mexican officials evicted Americans from their property in the disputed Mesilla Valley. When the U.S. Government did not act, Governor William Lane of New Mexico declared the Mesilla Valley part of the U.S. territory of New Mexico. Mexican President Antonio de Santa Anna responded by sending troops into the valley. Attempting to diffuse the situation, U.S. President Franklin Pierce sent James Gadsden, the new U.S. Minister to Mexico, to negotiate with Santa Anna. Secretary of State William Marcy instructed Gadsden to renegotiate a border that provided a route for a southern railroad, arrange for a release of U.S. financial obligations for Native American attacks, and settle the monetary claims between the countries related to the Garay project.
Mexican President Antonio de Santa Anna
With a great deal of difficulty resulting from the increasing strife between the northern and southern states, the U.S. Senate ratified a revised treaty on April 25, 1854. The new treaty reduced the amount paid to Mexico to $10 million and the land purchased to 29,670 square miles, and removed any mention of Native American attacks and private claims. President Pierce signed the treaty and Gadsden presented the new treaty to Santa Anna, who signed it on June 8, 1854.
After Gadsden’s Purchase a new border dispute caused tension over the United States’ payment, and the treaty failed to resolve the issues surrounding financial claims and border attacks. However, it did create the southern border of the present-day United States, despite the beliefs of the vast majority of policymakers at the time who thought the United States would eventually expand further into Mexico.

