On Dec. 30, 1853, the United States purchased from Mexico a strip of land south of the Gila River. This land, which formed part of the boundary of the two nations, today is part of Arizona and New Mexico.
Texas had revolted against the Mexican government in 1835. The following year, it became the Republic of Texas. In 1845, Texas was admitted as a U.S. state, and Mexico broke off relations with the United States. Because Americans believed in “manifest destiny” (a drive for territorial expansion), the United States wanted additional Mexican land. After a diplomatic mission failed, the Mexicans surprised and defeated a small group of American cavalry in territory claimed by both countries. On May 13, 1846, the United States declared war on Mexico.
The Mexican War (1846-1848) was a clear American victory. However, despite all of the American victories, Mexico refused to negotiate a peace treaty. Finally, in 1847, U.S. troops captured Mexico City, and Mexican President Antonio López de Santa Anna resigned shortly thereafter. (This was the same Santa Anna who had defeated the Texans at the Alamo.) Mexico established a new government, and it feared that it might lose even more territory if it did not accept the American demands. On Feb. 2, 1848, the two countries signed the Treat of Guadalupe Hidalgo, and the Mexican War ended.
As a result of the Mexican War, the United States had acquired a great deal of land from Mexico. But the Treaty of Guadalupe Hidalgo was unclear about the new boundary between the two countries. The purpose of the Gadsden Purchase was to provide a definite boundary and also give the United States better railroad access to the Pacific Ocean.
James Gadsden, the U.S. minister to Mexico, conducted the negotiations with Santa Anna, who had returned as the Mexican president earlier in 1853. Santa Anna rejected Gadsden’s proposal at first. However, the Mexican government desperately needed funds, and Santa Anna feared U.S. military action if he refused to sell the land.
The United States paid $10 million for the 29,640 square miles (76,770 square kilometers) in the purchase. The treaty of sale, the Gadsden Treaty, was signed on Dec. 30, 1853. The two countries ratified the treaty on June 30, 1854. Mexican unhappiness with the sale was one of the reasons Santa Anna was banished from Mexico in 1855.
In addition to the purchase, the Gadsden Treaty granted the United States the right to cross Mexico’s Isthmus of Tehuantepec, which provided a route between the Gulf of Mexico and the Pacific Ocean. The treaty also abolished a requirement that the United States protect Mexico from Indian attacks. The United States had agreed to that requirement in 1848 in the Treaty of Guadalupe Hidalgo.