what is this event?
Also known as "The Sale of La Mesilla" - United States acquired a region of present-day southern Arizona and southwestern New Mexico from Mexico by the Treaty of Mesilla - the region is also called Gadsden Purchase.
Gadsden Purchase
The Gadsden Purchase ( "The Sale of La Mesilla"), is a region of present-day southern Arizona and southwestern New Mexico that the United States acquired from Mexico by the Treaty of Mesilla, which took effect on June 8, 1854. The purchase included lands south of the Gila River and west of the Rio Grande where the U.S. wanted to build a transcontinental railroad along a deep southern route, which the Southern Pacific Railroad later completed in 1881–1883. The purchase also aimed to resolve other border issues.

The first draft was signed on December 30, 1853, by James Gadsden, U.S. ambassador to Mexico, and by Antonio López de Santa Anna, president of Mexico. The U.S. Senate voted in favor of ratifying it with amendments on April 25, 1854, and then transmitted it to President Franklin Pierce. Mexico's government and its General Congress or Congress of the Union took final approval action on June 8, 1854, when the treaty took effect. The purchase was the last substantial territorial acq
increased u.s. territory in present-day arizona and new mexico This event is called the Gadsden Purchase
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Gadsden Purchase [SEP] Introduction
The Gadsden Purchase ( "The Sale of La Mesilla"), is a region of present-day southern Arizona and southwestern New Mexico that the United States acquired from Mexico by the Treaty of Mesilla, which took effect on June 8, 1854. The purchase included lands south of the Gila River and west of the Rio Grande where the U.S. wanted to build a transcontinental railroad along a deep southern route, which the Southern Pacific Railroad later completed in 1881–1883. The purchase also aimed to resolve other border issues. The first draft was signed on December 30, 1853, by James Gadsden, U.S. ambassador to Mexico, and by Antonio López de Santa Anna, president of Mexico.