by Mary Gindling

Created on: January 16, 2010   Last Updated: January 17, 2010

Most Americans know at least something about the Louisiana Purchase. But there was another important land acquisition that added millions of acres to the states of Arizona and New Mexico and defined the southern borders of the Western United States. That acquisition is known as the Gadsden Purchase.

While the 1848 Treaty of Guadalupe Hidalgo ended the war between the United States and Mexico, tensions between the two countries remained high. Under the terms of the treaty, the United States was obligated to protect Mexico against Native American attacks in the Mesilla Valley, which was claimed by both countries. The Mexican government demanded monetary compensation for on-going attacks, but the United States refused on the grounds that they had not agreed to pay for damage caused by the Native Americans.

The tensions between the two nations complicated efforts by U.S. investors to find a southern route for a planned transcontinental railroad. The only possible routes passed through Mexican Territory, which was obviously not a viable choice. In 1847, while the Mexican-American war was still raging, the U.S. had attempted to buy the Isthmus of Tehuantepec to obtain a route from the Atlantic to the Pacific oceans. But Mexico had already granted the isthmus to Mexican citizen Don Jose de Garay, who planned to build colonies for Americans. Mexico’s president Juan Caballos subsequently revoked the grant, fearing that American colonists there would rebel just as they had in Texas.

In April 1853, Antonio de Santa Anna had once more become President of Mexico and, shortly afterward, Mexican officials forced Americans from their properties in the disputed Mesilla Valley. The U.S. government failed to act, so New Mexico’s Governor William Lane announced that the Mesilla Valley belonged to the Territory of New Mexico. Santa Anna sent troops into the valley to defend the Mexican claim.

Faced with the prospect of yet another war with Mexico. U.S. President Franklin Pierce sent James Gadsden, the newly created U.S. Minister to Mexico, to Mexico City. His instructions were to negotiate a new border that would allow the southern railroad to be built, to end the Mexican demand for reparations for Native American attacks, and to settle any monetary claims related to the Garay project.

As Gadsden prepared to meet with Santa Anna on September 25, 1853, Gadsden received further instructions from President Pierce. Christopher Ward, an agent for U.S. investors in the Garay

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