<Li> permission for the United States to intervene unilaterally "when it may feel sanctioned and warranted by the public or international law"; and </Li> <Li> a reduction of the territory to be acquired by 9,000 square miles (23,000 km) and dropping the price from $15 million (equivalent to $6.23 billion in 2016) to $10 million (equivalent to $4.15 billion in 2016). </Li> <P> This version of the treaty successfully passed the US Senate April 25, 1854, by a vote of 33 to 12 . The reduction in territory was an accommodation of northern senators who opposed the acquisition of additional slave territory . In the final vote, northerners split 12 to 12 . Gadsden took the revised treaty back to Santa Anna, who accepted the changes . The treaty went into effect June 30, 1854 . </P> <P> While the land was available for construction of a southern railroad, the issue had become too strongly associated with the sectional debate over slavery to receive federal funding . Roberson wrote: </P>

Who negotiated the purchase of the area south of gila river