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Cambodian soldiers with an anti-aircraft gun in Oddar Meanchey province (Tang Chhin Sothy/AFP via Getty Images)

Thailand-Cambodia clashes pose a serious test to ASEAN centrality

Border violence between two members undermines the bloc’s credibility and risks drawing in great power competition.

Khang Vu

28 July 20254 min read

ASEAN centrality is a concept in crisis. The bloc now faces a huge test as Thailand and Cambodia clash along the disputed border in the Emerald Triangle. Yet there is little sign that the Association of Southeast Asian Nations, either as an organisation or a venue, will play a crucial role in the resolution.

As 2025 chair, Malaysian Prime Minister Anwar Ibrahim has called on both sides to de-escalate and resolve the dispute the “ASEAN way”. Cambodia has instead referred the matter to the UN Security Council. Thailand wants to resolve the clash bilaterally and only after Cambodia stops its attacks.

The skirmish has undermined two key tenets of the ASEAN Treaty of Amity and Cooperation, which involve non-interference into internal affairs of member states and the renunciation of threats or the use of force. This latest crisis comes on top of ASEAN taking a sclerotic approach to the spillover effects of conflict in Myanmar as well as its continued failure to issue any joint communique over the South China Sea disputes.

ASEAN has often boasted that no member has fought a war against another member since the founding of the bloc in 1967. But the claim about peaceful relations was already tenuous. Between 2008 and 2011, Thailand and Cambodia did fight several deadly skirmishes in the area, which only ended after ASEAN’s then chair, Indonesia, with a mandate from the UN Security Council, mediated the dispute. Thailand and Cambodia only agreed to a ceasefire and the border dispute itself was not resolved.

The latest tension has been playing out for weeks, but ASEAN has shown little urgency in seeking a resolution. Cambodia’s leaking a private phone call between former Thai Prime Minister Paetongtarn Shinawatra and Cambodia’s former leader Hun Sen, also father of Cambodia’s present prime minister, has shaken Thai politics.

But it is the international dimension that most threatens the notion of ASEAN centrality and its long claim to nonalignment. Thailand and Cambodia are close security partners of the United States and China respectively. If ASEAN cannot mediate the conflict via regional mechanism, a great power intervention into the conflict risks sidelining ASEAN altogether.

A diplomatic settlement is the only option to guarantee long-term peace. But that will get much harder should the great powers get involved.

ASEAN should look back to the lessons of the Cambodia-Vietnam border war to prevent a regional issue from being internationalised to its own detriment. Neither country was an ASEAN member at the time, yet the experience still holds value in navigating the risks of the present.

Shortly after the Fall of Saigon in 1975, the Khmer Rouge launched several attacks against Vietnam-held islands off the Gulf of Thailand to reclaim ancient Khmer land that it deemed Vietnam had unlawfully annexed. Vietnam tried to settle the dispute by talking to the Khmer Rouge leaders and its Chinese backers. Only the Khmer Rouge later attacked Vietnam’s southwestern provinces in April 1977. Hanoi launched a limited counteroffensive into Cambodian territory later that same year.

The lack of progress in negotiations convinced Hanoi to ink an alliance treaty with the Soviet Union, to China’s dismay. Vietnam then launched a full-scale invasion of Cambodia to topple the Khmer Rouge in December 1978. Due to the Sino-Soviet split, both Moscow and Beijing were happy to provide support to their respective clients. The Cambodia-Vietnam border war turned into a struggle between the Soviet Union and China. The United States was subsequently drawn into the struggle with support for Thailand against Vietnam’s occupation of Cambodia.

It made for strange diplomatic bedfellows. ASEAN sided with China and the United States, backing the Khmer Rouge to keep the Cambodian seat at the United Nations against the Vietnam-supported People’s Republic of Kampuchea. It made Southeast Asia again a battleground for great power rivalry just a few years after the end of the Vietnam War, and the dispute would only be resolved after the Soviet Union and China mended relations beginning in 1986 and Vietnam slowly and formally ended its involvement in Cambodia in 1991, settling the border dispute. Vietnam only joined ASEAN in 1995 after Hanoi and the bloc dropped their hostile attitude toward each other.

The lessons for the Thailand-Cambodia border dispute of today are clear: the most obvious is the limited utility of military force. There is nothing to indicate that Thailand and Cambodia escalating the dispute can achieve a durable settlement. The conflict transforming into a personal feud between the Shinawatras and Hun Sen only makes concessions more politically costly.

A diplomatic settlement is the only option to guarantee long-term peace. But that will get much harder should the great powers get involved. The internationalisation of the Cambodia-Vietnam border dispute amid Cold War rivalries only hardened the dispute. It may be tempting for Thailand to reopen its bases to the US military (Thailand has not hosted a permanent US base since 1976) or Cambodia to grant China a stronger presence in the Ream naval base if the skirmish escalates. But this will only hurt Thai and Cambodian agency in settling the dispute.

The next lesson must be for ASEAN to assert its inclusive and mediating role in regional affairs. It must strive for a peaceful settlement, and illustrate that the ASEAN way truly can pass the test of managing intra-bloc disputes.

About the author

Khang Vu

Khang Vu is a visiting scholar in the Political Science Department at Boston College.

Topics

ASEAN Cambodia Thailand