How Thai-Cambodian clashes undermine ASEAN unity – Firstpost

Just days after the conclusion of the 46th ASEAN Summit in late May 2025, a deadly military clash erupted between Thailand and Cambodia, reigniting longstanding tensions over their disputed border. On May 28, a Cambodian soldier was killed in the Emerald Triangle region—a sensitive trijunction where the borders of Thailand, Cambodia, and Laos converge. This forested and mountainous region, near the Dângrêk Mountains and the Mekong River basin, has been a flashpoint due to ambiguous territorial claims dating back to the colonial era.

This latest skirmish has brought renewed attention to a simmering territorial dispute involving several ancient temple sites near the two countries’ shared border, including Ta Moan Thom, Ta Moan Tauch, Ta Krabei, and the Mom Bei area. The Cambodian government, led by PM Hun Manet, has declared its intention to bring the matter before the International Court of Justice (ICJ), while Thailand has reiterated its preference for bilateral dialogue.

In a move suggesting growing frustration, Cambodia announced that the upcoming June 14 Joint Border Committee (JBC) meeting with Thailand will proceed, but with a caveat: the four disputed areas will not be on the agenda. This has raised concerns about the effectiveness of bilateral forums in resolving deeper underlying tensions.

Despite Cambodia’s legal approach to the ICJ, critics question why it has not more actively sought ASEAN mediation. Pou Sothirak, a retired academic and senior advisor at the Cambodia Centre for Regional Studies, remarked, “Cambodia should call on ASEAN for mediation immediately—even if ASEAN has limitations—to show our solidarity with member states and our preference for peaceful means.”

The current escalation threatens to erode ASEAN unity at a time when the bloc seeks to present a united front in addressing regional security and economic challenges. The clash also coincides with increased nationalist sentiment in Thailand, where conservatives have expressed concern over recent discussions to jointly explore energy resources in undemarcated maritime zones. These talks have stirred fears of losing territory, such as the island of Koh Kood in the Gulf of Thailand, further complicating bilateral diplomacy.

In the immediate aftermath of the May 28 clash, Thailand closed two key tourist border crossings in Chanthaburi province, citing national security concerns. While the movement of Cambodian labourers and trade remains unaffected, six additional border checkpoints have shortened their operating hours, and restrictions on six-wheeled vehicles have been imposed. Thailand’s Defence Minister, Phumtham Wechayachai, confirmed an increased military presence in the border area, citing reports of Cambodian troop build-up.

Cambodian PM Hun Manet, while insisting that his country’s actions are defensive, stated that a formal complaint would be lodged with the ICJ. Tensions were aggravated by Cambodia’s refusal to comply with a Thai request to withdraw troops from the contested region, despite both nations having earlier agreed to ease tensions.

The current crisis is the latest in a series of confrontations between Thailand and Cambodia, reflecting deep-rooted historical and political complexities. The 817-kilometre border between the two countries, originally demarcated by the French in 1907 during their colonial administration of Cambodia, remains a source of contention, with several segments still or contested.

Previous flare-ups have occurred in 2011, 2013, and 2017, mostly around the Preah Vihear Temple area. While the ICJ ruled in 1962 that Cambodia had sovereignty over the Preah Vihear Temple, it did not resolve surrounding territorial ambiguities. The strategic and symbolic significance of these sites—many of which are perched on cliffs or lie in dense forest—continues to inflame nationalist passions on both sides.

Each clash exacts a humanitarian toll. Communities near the border are frequently displaced, local economies suffer disruptions, and the risk of full-scale conflict looms whenever minor confrontations escalate. Military skirmishes often involve small arms, mortars, and artillery, with poor communication and difficult terrain contributing to accidental engagements.

Several underlying factors fuel these recurring disputes. Chief among them is the legacy of ambiguous colonial-era boundaries. Nationalist pressures within both countries also play a significant role, often pushing governments to adopt uncompromising positions. Resource competition, especially in mineral-rich and forested areas, and speculation about untapped energy reserves add an economic dimension to the conflict. Meanwhile, military posturing, fortified camps, and patrols along the border ensure that even minor provocations can lead to dangerous escalations.

External mediation efforts have had limited success. ASEAN, although committed to regional peace and cooperation, struggles with internal divisions and institutional constraints. Its non-interference policy and consensus-based decision-making often inhibit decisive action. The ICJ has provided rulings, but enforcement remains weak, especially when national pride or domestic politics are at stake.

Thailand’s internal politics have also influenced the border situation. PM Paetongtarn Shinawatra’s government, already under pressure from a sluggish economy and rising US tariffs, has faced criticism from conservative factions over its approach to bilateral negotiations with Cambodia. In contrast, Thailand’s military has taken a more hawkish stance, recently issuing statements affirming readiness for a “high-level operation” if national sovereignty is perceived to be threatened.

Looking forward, a peaceful and lasting resolution to the Thai-Cambodian border dispute requires a multifaceted strategy. First, both countries must prioritise diplomatic dialogue and agree to clarify border demarcations through joint surveys and formal treaties. Second, ASEAN must be empowered to play a more active mediatory role, even if just as a symbolic gesture of regional solidarity. Third, implementing past ICJ rulings and exploring mechanisms for dispute resolution under international law should be at the forefront of future negotiations.

Additionally, confidence-building measures—such as joint military patrols, civilian demilitarised zones, and real-time communication channels—could reduce the risk of accidental clashes. Developmental cooperation along the border, including shared infrastructure projects and economic zones, could shift the focus from confrontation to mutual benefit.

Finally, domestic political leaders in both countries must work to temper nationalist rhetoric and resist the temptation to use the border issue for short-term political gain. Instead, they should emphasise the long-term benefits of peace, cooperation, and regional integration.

In conclusion, the recent clashes between Thailand and Cambodia underscore the fragility of peace along their shared border and the limitations of current dispute-resolution mechanisms. The situation presents a challenge not only to bilateral relations but also to ASEAN’s credibility as a forum for regional stability.

If Southeast Asia is to move forward as a cohesive and cooperative bloc, resolving historical disputes like this one is essential. Cambodia and Thailand must seize this moment to pursue a lasting resolution that prioritises peace, prosperity, and the well-being of their people over historical grievances and nationalist posturing.

The author is a former ambassador to Germany, Indonesia, Ethiopia, ASEAN and the African Union. He tweets @AmbGurjitSingh. Views expressed in the above piece are personal and solely those of the author. They do not necessarily reflect Firstpost’s views.