AKP Phnom Penh, August 31, 2026 --

Southeast Asia is increasingly becoming one of the central theatres in which the future regional order will be negotiated. Strategic competition between the United States and China is intensifying, maritime tensions remain unresolved, and technological rivalry and economic-security concerns are reshaping regional relations. For ASEAN, the challenge is not merely how to navigate between major powers, but how to preserve unity, strategic autonomy and relevance. Japan matters because its engagement with Southeast Asia combines strategic interests with development cooperation, economic partnership and sustained support for ASEAN-centred regionalism.

During my recent visit to Japan at the invitation of Japan’s Ministry of Foreign Affairs, I exchanged views with MOFA officials, scholars, think-tank experts and university professors on Japan-ASEAN relations, the updated Free and Open Indo-Pacific, Japan-China relations and the wider regional environment. These discussions reinforced an important point: Japan’s approach to Southeast Asia is best understood not simply as a response to China’s rise, but as part of a longer effort to build durable relationships, preserve an open regional order and strengthen the capacity of regional partners to make their own choices.

That longer history matters. The 1977 Fukuda Doctrine pledged that Japan would not become a military power, would build a “heart-to-heart” relationship with Southeast Asia and would engage ASEAN as an equal partner. More than four decades later, the vocabulary has evolved, but the emphasis on trust remains visible. The 2023 ASEAN-Japan Joint Vision Statement described the two sides as “Trusted Partners” and organised cooperation around intergenerational ties, co-creation of the future economy and society, and regional peace. This accumulated trust gives Japan diplomatic capital that cannot be measured only by trade or aid.

The updated FOIP should also be read through this broader lens. Japan now places greater emphasis on resilience, inclusiveness, diversity, openness and the rule of law, while stressing that regional countries should retain the “freedom to decide for themselves.” Its priority areas include economic infrastructure for the age of AI and data, resilient supply chains for energy and critical materials, public-private co-creation, connectivity, rule-sharing and security cooperation. For ASEAN, the key test is whether FOIP complements rather than competes with the ASEAN Outlook on the Indo-Pacific. Japan’s explicit support for mainstreaming the AOIP and strengthening ASEAN-led mechanisms is therefore significant.

This approach is especially relevant because Southeast Asian states generally do not want to reduce their foreign policies to a binary choice between Washington and Beijing. China is a major economic partner and immediate neighbour for much of the region, while the United States remains a leading security, technological and economic power. Japan, India, South Korea, the European Union and others further widen ASEAN’s external options. ASEAN members therefore seek an open regional environment in which they can cooperate with multiple partners without surrendering policy autonomy.

Japan’s own relationship with China illustrates why such balance is difficult but necessary. The bilateral relationship contains serious tensions over the East China Sea, Taiwan, military activities, export controls and economic security. Yet Japanese officials also emphasise the need to maintain dialogue, pursue a “constructive and stable” relationship, and cooperate where interests overlap. Scholarly analysis presented during my visit similarly highlighted continuing economic interdependence and the importance of avoiding a simple either-or framework between the United States and China. For Southeast Asia, this is instructive: strategic competition does not eliminate the need for coexistence, communication and selective cooperation.

ASEAN centrality therefore remains more than diplomatic symbolism. ASEAN-led mechanisms—the East Asia Summit, ASEAN Regional Forum, ASEAN Plus Three and the ASEAN Defence Ministers’ Meeting Plus—provide rare spaces where competing powers continue to sit at the same table. Their effectiveness should not be exaggerated, but neither should their preventive value be underestimated. When bilateral channels are strained, inclusive regional institutions can sustain communication, socialise expectations and reduce the risk that disagreement becomes confrontation.

Economic resilience is another area where Japan-ASEAN cooperation can become more concrete. Diversifying supply chains, improving digital infrastructure, strengthening energy and food security, expanding quality connectivity and developing higher-value industries can reduce vulnerability without requiring economic decoupling. Economic security should expand options, not become a new justification for fragmentation. For Cambodia and other developing ASEAN members, Japanese investment, infrastructure, skills development and technology transfer can also help narrow intra-ASEAN development gaps, which are themselves a source of institutional weakness.

The same logic applies to maritime and non-traditional security cooperation. Japan’s support for maritime domain awareness, coastguard capacity, cybersecurity, disaster response and international law can strengthen regional resilience. Yet capacity-building is most constructive when it enables states to defend legitimate interests, manage disputes peacefully and avoid unnecessary escalation. For smaller states, international law and competent institutions matter precisely because material power is unequal.

ASEAN, however, cannot outsource its centrality. External support from Japan is valuable, but ASEAN’s strategic relevance ultimately depends on its own unity, credibility and ability to respond to difficult issues. Centrality without capacity risks becoming ceremonial. ASEAN members must therefore strengthen internal consultation, narrow development gaps and resist pressures that turn national differences into permanent strategic divisions.

For Cambodia, Japan’s role is most useful when it enlarges rather than narrows strategic space. Closer cooperation with Japan is fully compatible with Cambodia’s independence, neutrality, diversified partnerships and commitment to ASEAN centrality. The objective should not be alignment against any major power, but stronger national and regional resilience.

The future Indo-Pacific will not be shaped by great-power rivalry alone. It will also be influenced by how ASEAN exercises agency and how partners such as Japan use their diplomatic, economic and institutional weight. The most sustainable regional order will be one in which rules constrain power, economic interdependence discourages confrontation, ASEAN remains an inclusive convening centre, and dialogue stays open even when strategic differences persist. In that search for stability, Japan’s most valuable contribution may be not to ask Southeast Asia to choose sides, but to help ensure that it retains meaningful choices.

By Kin Phea, an alternate member of Royal Academy of Cambodia and director-general of International Relations Institute of Cambodia