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How did the Gadsden Purchase change the U.S.-Mexico border after the Mexican-American War?

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How the Mexican-American War changed the U.S. forever — Mexican-American War Learn how the Mexican-American War ultimately pushed the United States closer to civil war.

The Gadsden Purchase of 1853 adjusted the U.S.-Mexico border established by the Treaty of Guadalupe Hidalgo following the Mexican-American War. While the 1848 treaty had set the boundary along the Gila River, the Gadsden Purchase transferred nearly 30,000 square miles of territory south of that river to the United States.123

This transaction, known in Mexico as the sale of the Mesilla Valley, was negotiated by U.S. minister James Gadsden to secure a more practical route for a southern transcontinental railroad to the Pacific. In exchange for $10 million, the United States acquired land that now constitutes parts of southern Arizona and southern New Mexico. This purchase finalized the continental expansion of the United States, extending the border further south than the limits established at the conclusion of the war in 1848.14325