Common Waters: Japan, South Korea, and Maritime Security Assistance in Southeast Asia

executive summary:This article proposes that Southeast Asia is an ideal space for cooperation between Japan and South Korea, given that both countries share strategic priorities in the region.main argumentAlthough Japan and South Korea's bilateral ties are typically defined by long-standing issues over historical issues and territorial disputes, each country shares a wide set of geopolitical interests, leading to an "Asian paradox" of mismatched priorities. This paradox is clearly visible in Southeast Asia. While Tokyo's strategic ties with the subregion, often via the Association of Southeast Asian Nations (ASEAN), are deeper and predate Seoul's, South Korea is increasingly expanding its own relations with the region alongside its growing security outreach across the Asia-Pacific. As a result, Japan's and South Korea's interests and activities are meeting in strategic spaces in Southeast Asia, such as the South China Sea and the Mekong River basin. Despite sharing common goals in these spaces, so far Seoul and Tokyo have not collaborated in their efforts. While many hurdles still limit direct security cooperation between Japan and South Korea, even indirect cooperation in shared strategic spaces in Southeast Asia could provide both countries an opportunity to build trust and provide security benefits to countries in Southeast Asia.policy implications• The U.S. can incentivize Japan–South Korea cooperation in Southeast Asia through the Quad Plus framework.• Expanding the General Security of Military Information Agreement between Japan and South Korea could be a method of increasing their cooperation in Southeast Asia.• To achieve greater cooperation toward these aims, the U.S. should support strategic latitude for Japan and South Korea in Southeast Asia.