[109][110]
Davis, an advocate of a southern transcontinental route, persuaded Pierce to send rail magnate James Gadsden to Mexico to buy land for a potential railroad. Gadsden was also charged with re-negotiating the provisions of the Treaty of Guadalupe Hidalgo which required the U.S. to prevent Native American raids into Mexico from New Mexico Territory. Gadsden negotiated a treaty with Mexican President Antonio López de Santa Anna in December 1853, purchasing a large swath of land to America's southwest. Negotiations were nearly derailed by William Walker's unauthorized expedition into Mexico, and so a clause was included charging the U.S. with combating future such attempts.[111][112] Congress reduced the Gadsden Purchase to the region now comprising southern Arizona and part of southern New Mexico; the price was cut from $15 million to $10 million. Congress also included a protection clause for a private citizen, Albert G. Sloo, whose interests were threatened by the purchase. Pierce opposed the use of the federal government to prop up private industry and did not endorse the final version of the treaty, which was ratified nonetheless.[113][112] The acquisition brought the contiguous United States to its present-day boundaries, excepting later minor adjustments.