Reconciling Cambodia and Thailand

Reconciliation through International Law

Conflict on the Border

On 23 July, three months after skirmishes between Thai and Cambodian border guards in a disputed border area between Thailand’s Ubon Ratchatani province and Cambodia’s Preah Vihear province, a Cambodian PMN-2 Soviet-origin landmine detonated during a Thai military patrol (Bangkok Post, 2025). It injured four Thai soldiers and took the right leg of one more.

Cambodia, a signatory to the 1997 Ottawa Mine Ban Treaty and one of the most heavily mined countries on earth, claims that this is the result of leftover ordnance from its civil war. Cambodia’s northwest border with Thailand remains heavily mined both from the Cambodian civil war and the short-lived People’s Republic of Kampuchea's (PRK) K5 containment plan (Landmine Monitor 2022, 2022). Ly Tuch, the Vice President of Cambodia’s demining governmental agency, The Cambodian Mine Action Authority, accused the mine incidents of being false-flag pretences for Thai aggression (Wee, 2025).

Notably, this is the largest military escalation since 2011 when border skirmishes broke out over the disputed Preah Vihear temple, a conflict rooted in ambiguities and conflicting narratives related to a jointly conducted 1907 border survey between Siam and the French colonial government.

Forming International Law

The border region conflict has ignited in the context of a century-old dispute between the two states over the border demarcation and a series of historically significant Hindu temples along it. Centrally, Preah Vihear, the subject of a 1962 International Court of Justice (ICJ) court ruling and a 2013 ICJ clarification, has been ruled on as under Cambodian sovereignty (UN News, 2013), but conflicts between customary and treaty law have drawn a large section of the border into doubt.

Thailand contests the temple according to a 1904 treaty that established the watershed as the border between the two states (Office of the Historian, n.d.). This principle, when applied to the modern border, would put the Temple squarely in Thai territory. However, a joint Siamese-French border commission established in 1904 created a series of border maps that did not apply this principle, which were accepted into official use by both states. The map delineating the Preah Vihear temple as on the Cambodian side was presented to Siam in 1908 (Plasai, 2013). While Siam had the opportunity to object to the treaty, its abstention created a legitimate expectation of the border status and facilitated its entry into customary law (International Court of Justice, 1951).

More specifically, developing international customary law has two requirements to enter into force and be codified by the ICJ: state practice and opinio juris. There must be both evidence of state behaviour that reflects a practice and a sense of legal obligation demonstrated to it. While the maps were not subject to a subsequent treaty's jurisdiction, Siam’s silence and own usage of the maps fulfilled both criteria for customary law formation upon which its later loss at the ICJ relied.

Just 2 weeks after the Thailand-Cambodia Joint Boundary Commission met for the first time in 13 years, Cambodia signalled it was planning to bring the rest of its border disputes to the ICJ, with or without Thailand (Cheang, 2025). Cambodia's new case would seek to clarify the Mom Bei area of Preah Vihear province and three more temples in the region: Tamone Thom, Tamone Touch, and Ta Krabey (Cambodian Ministry of Foreign Affairs, 2019). These sites are along the same disputed watershed line that Preah Vihear belongs to.

Bilateral and Multilateral Legal Strategies

Thailand prefers bilateral resolution mechanisms rather than multilateral ones. Thailand consistently advocates for negotiations solely passing through the Thailand-Cambodia Joint Boundary Commission (JBC), a strategy that Thailand also employs with Laos, successfully demarcating 96% of their joint land boundary to date. Thailand seeks to negotiate with Cambodia bilaterally in a similar way, and while the JBC meets infrequently, the latest round of negotiations yielded tangible results. The JBC jointly resolved a series of earlier fact-finding missions and approved a number of next steps in survey and demarcation work. According to Thailand, working outside of this mechanism is “contrary to the spirit of good neighbourliness" (Thai Ministry of Foreign Affairs, 2025).

Cambodia is relatively more reliant on multilateral frameworks for its border resolution with Thailand. Just a week after the JBC concluded its round of negotiations, the Cambodian Ministry of Foreign Affairs held the inaugural meeting of its document preparation committee against Thailand in the ICJ (Cambodian Ministry of Foreign Affairs, 2019). Cambodia likely views this approach as more favourable to its position based on its past relative success in the past in the ICJ in 1962 and again in 2013.

Cambodia’s dual-track legal approach is an explicit strategy to mix short-term, medium-term, and long-term legal strategies to resolve the legal ownership question over its borders (Agence Kampuchea Presse - AKP, 2026). Its mixed-method approach to ‘reclaiming its territory’ puts long-term pressure on Thailand in bilateral negotiations, knowing that it has already lost its past two cases in the ICJ. Even if Thailand no longer accepts the ICJ’s compulsory jurisdiction (Bangkok Post, 2025), a win for Cambodia could bolster the perceived legitimacy of its claims on the border and provide some leverage to achieve more favourable resolutions with the larger state to its northwest.

The Importance of Geography

For Cambodia, its northwest border and the Dongrak mountains (Dangrek in Khmer) with Thailand are a significant geographic sensitivity and a geographic barrier that dominates Cambodia’s low-lying plains to the south. While the sprawling Khmer empire once stretched far north into Thailand along the Ancient Khmer Highway to the city of Phimai, the low-lying mountain range is now the last barrier that separates the two states. While the range slopes slowly northward, losing control of the Dangrek’s sharp southward cliffs would physically box in Cambodia, not to mention cause national humiliation by losing the numerous Khmer temples that still dot the region. It also involves cultural sensitivities related to the 1979 Dangrek Genocide, where Thai soldiers forced approximately 40,000 Cambodian refugees at gunpoint off the heavily mined and trapped Dangrek cliffs just east of Preah Vihear (Arzoo Osanloo & Cabeiri deBergh Robinson, 2024, pp. 84–97). The incident still remains raw in the memories of many Cambodians (Hinton, 2006).

For Thailand, the range has historically been a source of significant insecurity for a number of reasons, but physically, its largely undeveloped and forested terrain has allowed the mountains to flourish as a zone for illegal logging and past banditry and serve as the final stronghold of the Khmer Rouge well into the 1990s. Psychologically and politically, Thailand’s perceived loss of territory following the 1962 ICJ ruling by domestic nationalist actors constrains the ruling party’s possible concessions in its negotiations with Cambodia.

Intranational Politics, International Law, and Peace

In 2008, when Cambodia applied for Preah Vihear to become a UNESCO World Heritage Site, the contemporary opposition party, the People’s Alliance for Democracy (colloquially known as ‘Yellow Shirts’ or PAD), rallied nationalist sentiment against the reigning People’s Power Party (PPP) headed by the Prime Minister Samak Sundararavej and the former Prime Minister Thaksin Shinawatra (Hiebert & Killian, 2013), a staple of Thai politics since his meteoric rise to power in the late 1990s. When Samak’s foreign minister assented to the Cambodian application, organised protests from the PAD swept through the nation, and the PPP shifted towards nationalism to keep up with the zeitgeist. The situation worsened when, after the application was approved by UNESCO, hundreds of Thai and Cambodian soldiers converged on the temple and the surrounding disputed forest (Ciorciari, 2009).

This posed an electoral disaster for the PPP, and the issue of Thailand’s Cambodian border continues to be an enduring topic in Thai politics, particularly with nationalist constituencies. Pheu Thai, the successor to the now-defunct PPP, also suffered a decisive electoral defeat in the September 2025 elections in Sisaket, a province that borders Cambodia and is particularly sensitive to electoral issues about weak border management. Pheu Thai’s relatively light-touch approach to the border and liberal democratic posture is losing significant ground to the nationalist and national-security-focused centre-right Bhumjaithai party.

In June of 2025, Paetongtarn Shinawatra, daughter of Thaksin Shinawatra and head of the Pheu Thai party, discussed the border dispute with Hun Sen, Cambodia’s former leader. The recording of the call, leaked by Hun Sen himself, showed her conciliatory tone and critique of elements within the Thai military command. While Hun Sen called for leadership change in Thailand alongside the leak, this nonetheless demonstrates a disconnect between the political leanings of Thai leadership and their electoral incentives.

While yet understudied, Cambodia’s domestic politics are also wrapped up in the Preah Vihear legal dispute and the country’s border dispute with Thailand more broadly. In the ten years leading up to the 2013 ICJ case, Prime Minister Hun Sen, having first assumed power in 1985, repeatedly invoked the Preah Vihear issue, including appeals to international law in the months preceding national elections and employed anti-Thai nationalistic rhetoric to maintain political power (Rattanasengchanh, 2017).

While Cambodia currently stands to gain more than Thailand by working through the international legal system, they both have a vested interest in maintaining a low-intensity border conflict to bolster their government’s domestic legitimacy, particularly when seen through a first-image perspective à la Kenneth Waltz (Wagener, 2011). To resolve the conflict would no doubt either bring about their domestic political ruin or escalate tensions in their bordering state to a flashpoint, something neither side wants to risk. While nationalism is an important tool of their politics, outright nationalistic warfare is in neither economic nor political interests; hence, Cambodia’s nationalistic domestic signalling while relying on legalistic arguments for the slow resolution of the conflict by an international body.

Thailand, on the other hand, represents a significantly more powerful military force and would be less concerned about provoking nationalist sentiment in Cambodia by resolving the issue. Consequently, a bilateral resolution would almost certainly tilt the balance of negotiation in Thailand’s favour, given that the Cambodian international legal claim is generally considered to be more robust. Its primary concern would be with regional instability and exacerbating its existing refugee issue from the current low-intensity conflict, something it can generally avoid through bilateral negotiations that give an advantage to Thailand. A multilateral solution would certainly inflame its domestic base, something Shinawatra outright admitted she was not interested in.

Conclusion

The Thailand-Cambodia border dispute is not just a legal dispute over an ambiguous colonial boundary line; it is a simmering low-level military conflict that has an important place in the post-colonial zeitgeist of both states. Neither side sees outright war as beneficial, and the structural and political incentives that sustain the conflict remain firmly in place. For Cambodia, they are walking a line where they must both maintain nationalistic fervour while not letting it overflow into war, while keeping their eye on their ultimate goal of legitimising their position through the international court system. For Thailand, the Shinawatra political dynasty is mostly interested in finding a bilateral solution to the border and keeping its own nationalistic and military tendencies at bay. However, domestic nationalism has become a powerful tool for opposition parties to use as a wedge issue to gain power.

Both sides benefit from nominal peace, and ultimately, that can only be achieved within the confines of working through bilateral or multilateral treaty law or arbitrative law in the ICJ. Domestic incentives complicate this process because each state is incentivised to prioritise different legal channels with different implications on the predicted outcome. The legal methods work and have worked in the past, but often reflect political willingness in the party countries rather than the efficacy of the mechanisms themselves. Memories of national humiliation on both sides must be resolved before domestic peace can spill out into international cooperation.

References

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