The purpose of this thesis is to analyze the transformation of U.S.-Mexican relations throughout the nineteenth century and its impact on the border during the administrations of James K. Polk and Rutherford B. Hayes. This transformation is exemplified by the movement away from hostile interactions during Polk's presidency to the cooperative nature that arose between Hayes and, then President of Mexico, Porfirio Diaz. In addition, another aim was to place the importance of the public sphere in framing the policy making of the United States and Mexican governments. The thesis focused upon the research surrounding Polk, Hayes, and their interactions with Mexico during their terms as president. The secondary materials were supplemented with corresponding primary source material from the presidents as well as their close advisors such as newspaper articles, correspondences, and speeches from both the United States and Mexico. The conclusion of the work demonstrates that the transformation in the border, first, the United States to become the dominant power on the continent, ending its rivalry with Mexico. Second, the ability of Porfirio Diaz to bring some stability to the Mexican political structure that permitted him to work in conjunction with the United States to control the border in exchange for recognition. Third, the increase in economic ties of the United States and Mexico that made war an unprofitable and dangerous outcome for both countries. Last, the difference in the president's personalities, Polk being ambitious, while Hayes following a cautious policy, as well as the fading of American expansionism and the concept of "manifest destiny."