During the third month of the 30th year (1551) of the Jiajing era (1522-1556), the Ming government decided to offer a trade agreement to the Mongols led by Altan Khan, which would set up markets (mashi) where Mongolian horses would be traded for valuable Chinese commodities. This paper explores the political history of the late phase of the era through an analysis of the decisionmaking process leading up to the Ming government recognizing trade with Altan Khan, while continuing to refuse a long-standing demand to grant the Mongols tributary status. The research to date on the political situation at the time understands it as a period of political stagnation attributed to Emperor Shizong's withdrawal from governmental affairs and incompetence on the part of Yan Song, senior officer of the Grand Secretariat. Moreover, recent attempts to reexamine the situation have still not been able to produce a complete picture of what exactly was happening on the contemporary poltical scene in concrete terms. The opportunity to offer the trade agreement was furnished ironically by Shizong's increasing desire to conduct a military campaign against Altan Khan. During the eighth month of 1550, after Altan's army had surrounded Beijing (the so-called Gengxu zhibian) in protest of being refused tributary status, Shizong ordered that plans be drawn up for a punitive expedition against the Mongols. Although such a campaign was clearly unrealistic, Yan Song, other central bureaucrats, and the supreme commander and grand coordinator of the northern region went through the motions ouot of respect to Shizong's will, but in reality took every action possible to avoid such a campaign. While respect was shown for Shizong's refutation of tribute relations with the Mongols as an attitude consistent with the ideology supporting the traditional Chinese world order, attempts to satisfy Mongol's material demands by means other than "tributary trade" and thus pacify the unrest threatening China's borders gave birth to the idea of a "mashi" trade arrangement. The idea caused virulent opposition from government officials outraged by such a display of impudence toward the will of the emperor, but as the debate raged on, the proponents after several attempts finally persuaded Shizong, and a decision was reached to set up the "mashi" trade. However, due to such factors as Shizong's obstinate attitude and the fiscal situation on the ground, it became impossible to generate a scale of trade sufficient to satisfy Mongol demand, leading to an escalation of Mongol attacks. Consequently, after it became apparent that the hopes of Yan Song and his cohorts were unattainable, the "mashi" trade agreement was ended in the ninth month of 1522. From his investigation of this turn of events, the author concludes that the political history of the Jiajing Era should be placed in the context of a group of policy makers confronted with an emperor's stubborn espousal of ideals in no way reflecting reality and thus trying to bring the situation into a soft landing by navigating for areas of compromise linking political ideals with present reality. [ABSTRACT FROM AUTHOR]