The original plans of the purchase called for a much larger portion of land to be acquired from Mexico extending far enough South to encompass Baja California. These original boundaries were not only opposed by the Mexican people, but also by anti-Slavery senators who saw this as a move towards more slave territory. Even the small final strip of land that was finally acquired was enough to anger the Mexican people who watched as Antonio Lopez de Santa Anna squandered the money. This would be one of the major contributing factors that lead to the end of Santa Anna's political career.
On the Sonoita River in present-day southern Arizona, the United States Army established Fort Buchanan on November 17, 1856 in order to help control new land.