Secretary of War Jefferson Davis, an advocate of a southern transcontinental railroad route, persuaded President Pierce to send rail magnate James Gadsden to Mexico to buy land for a potential railroad. Gadsden was also charged with re-negotiating provisions of the Treaty of Guadalupe Hidalgo which required the U.S. to prevent Native American raids into Mexico from New Mexico Territory. Pierce authorized Gadsden to negotiate a treaty offering $50 million for large portions of Northern Mexico, including all of Baja California. Gadsden ultimately concluded a less far-reaching treaty with Mexican President Antonio López de Santa Anna in December 1853, purchasing a portion of the Mexican state of Sonora. 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. Other provisions in the treaty included U.S. assumption of all private claims by American citizens against the Mexican government, and American access to the Isthmus of Tehuantepec for transit. Pierce was disappointed by the treaty, and Gadsden would later claim that, if not for Walker's expedition, Mexico would have ceded the Baja California Peninsula and more of the state of Sonora. The treaty received a hostile reception from northern congressmen, many of whom saw it as another move designed to benefit the Slave Power. Congress reduced the Gadsden Purchase to the region now comprising southern Arizona and part of southern New Mexico; the original treaty had ceded a port on the Gulf of California to the United States. Congress also reduced the amount of money being paid to Mexico from $15 million to $10 million, and 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. The acquisition brought the contiguous United States to its present-day boundaries, excepting later minor adjustments. In mid-1848, President Polk authorized his ambassador to Spain, Romulus Mitchell Saunders, to negotiate the purchase of Cuba and offer Spain up to $100 million, an astounding sum at the time for one territory, equal to $ in present-day terms. Cuba was close to the United States and had slavery, so the idea appealed to Southerners but was unwelcome in the North. However, Spain was still making huge profits in Cuba (notably in sugar, molasses, rum, and tobacco), and thus the Spanish government rejected Saunders' overtures.