Defensive Realism and Japan’s Approach toward Korean Reunification
Victor D. Cha
One of the most underestimated yet critical variables in the future of the United States– Republic of Korea (ROK) alliance is the role of Japan. Arguably, from a U.S. perspective any future conceptions of a U.S.–Korea alliance would necessarily incorporate Japan as an integral component. During the Cold War, the Japan–ROK axis facilitated the American presence as an Asia–Pacific power and security guarantor. In the post–Cold War era, outcomes in the Japan–Korea (united or still divided) relationship remain critical to the shape of future balance of power dynamics in the region, and with it the future American security presence.
In spite of its importance, Japan's strategic preferences with regard to the Korean Peninsula and the U.S.–Korea alliance are the object of much contention and little consensus. Western scholarly views of Japanese grand strategy differ dramatically from those held in Asia. Moreover, the differences in these views have real ramifications for how one thinks about Japan's role in relation to a future U.S.–Korea alliance.
Arguments in the West, largely from the "constructivist" school of thought in international relations theory, focus on Japanese "postwar pacifism." This view predicts little substantive change in Japanese strategy or constitutional constraints on the use of force, and for this reason, little likely change in Japan's continued reliance on the United States security umbrella and the U.S.–Japan–Korea alliance framework. By contrast, arguments in Asia are informed by a "realist" view of Japanese intentions. This school argues that rearmament and independence in Japan's future security posture is inevitable. This, in turn, could mean a more competitive relationship with Korea and problems for the U.S.–Korea alliance.
This essay argues that both of these views are unsatisfactory. The former constructivist view has been rendered highly questionable by recent events and changes in Japanese security behavior. The latter realist view, moreover, is greatly underspecified. The type of realism that drives Japanese thinking is as important as the observation, as Mike Green and Ben Self have argued, that there exists a "reluctant realist" streak in Japan.  Japan's grand strategy toward the Korean Peninsula and the alliance is informed by realist tenets, but these are "defensive realist" tenets rather than "offensive realist" ones. This difference is critical because defensive realism, as it informs Japanese strategic choices, offers a far more optimistic outlook on Japan's support of the U.S.–Korea alliance than offensive realism.
The accepted scholarly and largely Western view of ...
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For other different realist interpretations of Japanese foreign policy, see Eric Heginbotham and
Richard Samuels, "Mercantile Realism and Japanese Foreign Policy,” International Security, vol. 22,
no.4 (Spring 1998), pp. 171–203; Reinhard Drifte, Japan’s Foreign Policy in the 1990s, N.Y.: St. Martins,
1996; Kenneth Pyle, The Japanese Question: Power and Purpose in a New Era, Washington, D.C.: AEI,
1996; and Michael Green and Benjamin Self, "Japan’s Changing China Policy: From Commercial Liberalism
to Reluctant Realism,” Survival, vol. 38, no. 2 (Summer 1996): pp. 35–58.