Who is fueling tensions in the South China Sea: The political logic behind Japan-Philippines security cooperation

Editor's note: Xu Weijun is an associate research professor at the Institute of Public Policy, South China University of Technology. His research interests include East Asian international relations, nationalism, Chinese diplomacy and China-US relations. The article reflects the author's opinions and not necessarily those of CGTN.

On July 12, 2026, Japan, the Philippines, the United States, and 11 other countries released a joint statement commemorating the 10th anniversary of the "South China Sea arbitration award," openly endorsing maritime and territorial claims unilaterally advanced by the Philippines. By exploiting this symbolic occasion, Japan, the Philippines, and other countries launched a new round of political mobilization and bloc-building. 

Since the release of the so-called award, its practical implications have extended far beyond the legal and maritime disputes between China and the Philippines. It has increasingly become a policy tool through which external powers intervene in South China Sea affairs and reshape the regional security landscape.

Japan's deepening involvement deserves particular attention. In recent years, Japan–Philippines security cooperation has expanded from maritime law-enforcement assistance to multiple dimensions, including troop access, joint exercises and training, defence equipment transfers, and multilateral coordination. Following the entry into force of the Reciprocal Access Agreement in September 2025, the two countries signed an Acquisition and Cross-Servicing Agreement in January 2026, thereby continuously upgrading their institutional framework for security cooperation. In April 2026, Japan dispatched about 1,400 Self-Defense Forces (SDF) personnel to participate in the US-Philippines Balikatan joint military exercise, whilst maritime cooperation activities under the Japan-Philippines-US and Japan-US-Australia-Philippines frameworks have also been steadily increasing. After lifting restrictions on defence equipment exports, the leaders of Japan and the Philippines reached further consensus in May 2026 to promote the transfer of destroyers, the TC-90, and radar systems to the Philippines. Therefore, Japan's involvement in South China Sea affairs has shifted from diplomatic statements and capacity-building to a more operational and institutionalized military arrangement.

Japan's accelerating involvement in South China Sea affairs is primarily motivated by its attempt to foster a security framework linking the South China Sea with the East China Sea and the Taiwan Strait. By repeatedly promoting the narrative of a shared threat posed by so-called Chinese maritime coercion, Japan seeks to extend its security perimeter further south-west and create external justifications for strengthening its military capabilities, expanding defence equipment exports, and relaxing restrictions on the SDF's overseas operations. Secondly, Japan intends to use the Philippines as a strategic fulcrum to embed the Japan-US alliance, the "Free and Open Indo-Pacific" vision, and minilateral security arrangements more deeply in Southeast Asia, thereby enhancing its influence in regional security affairs. Thirdly, by supporting the so-called award, Japan deliberately seeks to cultivate an image as a "defender of rules." It attempts to link legal discourse with geopolitical competition and mobilize more countries to participate in diplomatic pressure and strategic containment directed against China.

The Philippines, for its part, is strengthening its security alignment with Japan in an attempt to use external powers such as Japan, the United States and Australia to compensate for its own limited maritime capabilities, increase its leverage in bargaining with China, and transform the so-called award into a long-term diplomatic resource. For the Marcos administration, strengthening external security cooperation not only responds to domestic nationalist sentiment but also expands its room for manoeuvre in the event of maritime confrontations. However, should the Philippines come to regard the support of its allies as a security endorsement for frontline operations, it may undertake increasingly risky probing actions. External powers may also view specific maritime incidents as opportunities to test alliance credibility and expand their military presence, thereby triggering new security crises in the South China Sea.

The continued deepening of Japan-Philippines security alignment will have several direct implications for the situation in the South China Sea. First, it exacerbates the security dilemma in the region. As the number of warships, military aircraft, coastguard vessels and joint exercises increases, the frequency and complexity of encounters at sea and in the air will continue to rise. Accidental collisions and frictions will therefore be more likely to escalate into security crises between countries or even at the alliance level. Second, it pushes the South China Sea disputes towards bloc-based confrontation. Specific disputes that should be resolved through negotiations between the directly concerned parties are being reframed as regional issues requiring countries to "jointly oppose unilateral actions." This exerts greater pressure on other ASEAN countries to choose a side. Third, it erodes ASEAN's central role in regional governance. Relevant ASEAN documents emphasise the maintenance of regional stability through dialogue and cooperation rather than confrontation, call on all parties to exercise restraint, and promote the early conclusion of an effective and substantive Code of Conduct in the South China Sea. If the involvement of external military powers continues to deepen, negotiations over the Code of Conduct will become increasingly vulnerable to interference from major-power competition and alliance politics.

Peace and stability in the South China Sea cannot be built on continuously expanding military deployments and bloc-based deterrence. China neither accepts nor recognizes the so-called award and maintains that disputes should be resolved through negotiation and consultation among the directly concerned countries. This position fundamentally differs from the legal and political narratives constructed by Japan and the Philippines around the "award." To genuinely maintain peace and stability in the South China Sea, countries in the region should continue to implement the Declaration on the Conduct of Parties in the South China Sea, accelerate consultations on a Code of Conduct in the South China Sea, improve maritime and aerial communication mechanisms and emergency-response arrangements, and fully respect China's territorial sovereignty and maritime rights and interests in the South China Sea. External countries may provide regional public goods in areas such as maritime search and rescue, disaster response, environmental protection, and navigational safety. They should not, however, turn the South China Sea into a new frontier for demonstrating military presence or constructing exclusive security blocs. Only by returning to the path of dialogue, restraint, and cooperation can we prevent maritime disputes from being further instrumentalised and polarised, and truly preserve an open, inclusive and peaceful regional environment.