In an age of increasingly complex security situations around the world, it is essential that students and practitioners understand alliances and minilateral security mechanisms. Partnership within Hierarchy examines, in depth, the troubled evolution of the US–Japan–South Korea security triangle from the Cold War period to the present time. Referencing a voluminous amount of declassified documents in three different languages, Sung Chull Kim, through six case studies, delves into the common questions arising in different historical periods, such as who should pay costs, what to commit, and why. Burden sharing and commitment, Kim shows, emerged as the main subject of competing expectations and disagreements arising between the capable middle power Japan and the weak power South Korea. Kim details how the dominant power, the United States, has controlled the red lines and intervened in the disputes, the result of which is in most instances a balancing effect for the triangle. In this vein, he persuasively accounts for why historical disputes between Japan and South Korea, which submerged during the Cold War, reverberate today when asymmetry between the two is substantially balanced.