Japan and the Republic of Korea (ROK) have been two of the most critical pillars of peace, stability, and prosperity in the Asia-Pacific region for the past thirty years. At the same time, their relationship has fluctuated markedly and unpredictably. Despite the existence of a common ally in the United States and common security threats from the former Soviet Union, China, and North Korea, bilateral relations between Japan and South Korea have been persistently marred by friction.

In the first in-depth study of this puzzling relationship in over fifteen years, the author compares the commonly accepted explanation for this relationship—historical enmity—with one that focuses on policies of the United States as the key driver of Japan-ROK relations. He finds that while history and emotion certainly affect the ways in which Japanese and Koreans regard each other, cooperation and dissension in the relationship are better understood through what he calls a “quasi-alliance” model: two states that remain unallied but have a third party as a common ally.

This model finds that the “normal” state of Japan-ROK relations is characterized by friction that stems not only from history, but also from fundamental asymmetries in Japanese and Korean expectations of support from each other. The author shows, however, that in periods when the American defense commitment to the region is weak, Japan-ROK relations exhibit significantly less contention over bilateral issues. Without the prop of U.S. assistance, the two countries are seemingly willing to overlook the usual causes of friction and to adopt a more pragmatic approach. The author discusses the effects of democratization and the post-Cold War era on the triangular relationship, and addresses the prospects of a united Korea and its future relations with Japan, the United States, and China.

The book covers the period from 1965 to 1998 and draws on recently declassified U.S. documents, internal Korean government documents, and interviews with former policy makers in the United States, Japan, and Korea.