Why, in July 1991, did Japan suddenly reverse years of opposition to regional security multilateralism in East Asia, and propose a multilateral security dialogue? This study argues that two factors largely account for the so-called Nakayama proposal. First, after the Gulf War and in the midst of Soviet collapse, Japan concluded that it would have to play a larger international security role. Second, Japan realized that as a consequence it would need to expand its efforts to reassure Asian countries mistrustful of Japanese military power as a result of historical experience. Japanese policy-makers thus came to conceive of a multilateral security dialogue as a means for reassuring Asian countries about its plan to send troops overseas to participate in United Nations peacekeeping. Secondary factors contributing to Japan's decision to promote security multilateralism include the declining Soviet threat, fear of American withdrawal, and competition from other countries with differing conceptions of what form security multilateralism should assume. [ABSTRACT FROM AUTHOR]