It is conventional wisdom that great powers are overwhelmingly likely to win negotiations with weaker powers in international relations under anarchy. It is also difficult to imagine the situation that the dominant party concedes to the subordinate party and that the latter keeps taking a firm stand against the former. However, this situation happened in the defense burden-sharing negotiations between the Republic of Korea and the United States in 2013. It seems hard to explain the puzzle with the mainstream international relations theories because they generally uphold the conventional wisdom. They cannot provide us with an adequate explanation of where the subordinate’s supremacy of bargaining power derives from, in an asymmetric relationship, and how the negotiation reaches a conclusion. This study draws on the two-level game theory to explain the outcome of the ROK-U.S. negotiations. The two-level game approach emphasizes not only the role of the international level actors but also the interactions among stakeholders at the domestic level. The explanation develops the concept of the “win-set” in two-level games defined as the set of all possible international level agreements that would gain necessary majority among principal domestic constituents. This thesis shows how this ratification process encouraged the subordinate South Korea to overcome pressure from the dominant U.S. that strongly demanded considerable increase in military cost-sharing. In response to Korea’s efforts, the U.S. also focused on how it could successfully coerce South Korea to accept its demand for “fair” contributions. In other words, the allies respectively implemented strategies to lead the negotiations to their advantage in order to reduce its own win-sets and enlarge the opponent’s win-sets. Through the two-level game approach that illuminates the nature of negotiation as well as a source of bargaining power, this research demonstrates what strategies the members of the transpacific alliance exercised and how they affected the result of the burden-sharing negotiations. The analysis has implications for other cases which are particularly relevant in the context of the growing tendency on the part of the U.S. government to demand that its allies increase their contributions to mutual defense.