Recently, Cambodia is planning to file a case at the International Court of Justice (ICJ) over the border issue with Thailand following the military clash on 28th May 2025, which led to the death of a Cambodian soldier at Emerald Triangle. The Emerald Triangle, a trijunction bordering Laos, Cambodia, and Thailand, is an intact monsoon forest near the Dângrêk Mountains and the Mekong River basin. In South Asia, the land borders are demarcated based on river basins by the British colonial treaties. For example, the Kali River forms a natural border between India and Nepal; the border conflict is natural due to the shifting nature of river basins. Contrarily, in Southeast Asia, the French colonial treaty signed in 1904 made the mountains a point of demarcation. The Franco-Siamese 1904 Treaty formed the base in the 20th century to define the flux in the Thai-Cambodia borders, and an understanding was arrived at by this treaty of identifying the Dângrêk Mountains as the barrier creating borders between French Indochina (modern Cambodia and Laos) and Siam (modern Thailand). However, the exact border demarcation—exactly where?—was left to the mixed commission. Such omission has led to the century-old border conflict between Thailand and Cambodia, which makes this border the most volatile in Southeast Asia. Here are some questions, moots: How do differing interpretations of colonial cartography shape modern territorial claims between Thailand and Cambodia? How have historical rulings by the International Court of Justice (e.g., the 1962 Preah Vihear case) shaped current legal strategies in Cambodia and Thailand?
COLONIAL CARTOGRAPHY SHAPING MODERN THAI-CAMBODIA BORDER CLAIMS
The territorial disputes between Thailand and Cambodia, particularly concerning the Preah Vihear Temple, underscore the enduring impact of colonial cartography on contemporary Southeast Asian geopolitics. These disputes are rooted in differing interpretations of early 20th-century treaties and maps, which continue to influence national boundaries and bilateral relations. In the early 1900s, the Franco-Siamese treaties aimed to delineate the borders between Siam (modern-day Thailand) and French Indochina (encompassing present-day Cambodia and Laos). The 1904 treaty stipulated that the boundary would follow the natural watershed line of the Dângrêk Mountains. However, the subsequent 1907 map produced by French surveyors deviated from this principle, placing the Preah Vihear Temple within Cambodian territory. Thailand later contested this, arguing that the map was not officially sanctioned by the joint commission established to oversee the demarcation.
The ambiguity surrounding the temple’s location led to prolonged disputes. In 1962, the International Court of Justice (ICJ) adjudicated the matter, ruling in favor of Cambodia based on Thailand’s prior acceptance and use of the 1907 map without objection for several decades. The court emphasized that Thailand had acquiesced to the map’s delineation, thereby ceding any claim over the temple. Despite this ruling, tensions resurfaced in 2008 when Cambodia sought UNESCO World Heritage status for the temple, leading to renewed military clashes and diplomatic strains.
Interestingly, Thailand’s border with Laos, a product of colonial treaties, has remained relatively peaceful. The Franco-Siamese agreements clearly defined this boundary along the Mekong River, leaving little room for dispute. The absence of significant cultural or historical sites in the immediate border areas further reduced potential flashpoints. This contrast highlights how clear demarcations and the lack of contentious landmarks can contribute to stable international borders. The Preah Vihear Temple holds profound cultural and historical significance for both nations. For Cambodia, it symbolizes the grandeur of the Khmer Empire and national heritage. Its proximity and historical ties evoke a sense of shared cultural legacy for Thailand. This duality has fueled nationalist sentiments, complicating diplomatic efforts and turning the temple into a symbol of sovereignty and identity for both countries.
ICJ RULING IN 1961 AND 2013 ON BORDER ISSUES—WHY NOT SETTLED?
The International Court of Justice (ICJ) issued two significant rulings regarding the Preah Vihear Temple dispute between Cambodia and Thailand in 1962 and 2013. Despite these decisions, the border conflict remains unresolved, with recent developments indicating a potential new case at the ICJ. This persistent dispute underscores the complexities of interpreting historical treaties and maps and the influence of nationalistic sentiments on international legal processes. In 1962, the ICJ adjudicated the sovereignty over the Preah Vihear Temple, situated atop the Dângrêk Mountains. The court ruled in favor of Cambodia in a 9 to 3 decision, citing Thailand’s prior acceptance of a French-drawn map that placed the temple within Cambodian territory. The judgment mandated Thailand to withdraw its military forces from the temple area and return any artifacts removed since 1954. However, the ruling did not explicitly delineate the surrounding border, leaving room for future disputes over adjacent areas.
Decades later, ambiguities persisted regarding the extent of Cambodian sovereignty around the temple. In 2013, the ICJ provided an interpretation of its 1962 judgment, affirming that Cambodia held sovereignty over the entire promontory of Preah Vihear, as defined by the Annex I map. The court clarified that Thailand must withdraw its military personnel from this area. However, the ICJ refrained from addressing broader territorial claims, such as the nearby Phnom Trap Hill, leaving certain disputes unresolved.
Despite these rulings, tensions have persisted along the Cambodia-Thailand border. In May 2025, a Cambodian soldier was killed during a military clash near Morokot village in Preah Vihear province. In response, Cambodia announced plans to seek a new ruling from the ICJ to resolve ongoing border disputes, including areas surrounding the Ta Moan Thom, Ta Moan Toch, and Ta Kro Bei temples. Cambodian Prime Minister Hun Manet emphasized the need for a definitive legal resolution to prevent further conflicts. The Preah Vihear dispute has been a focal point of nationalistic fervor in both countries. The 1962 ICJ ruling remains a contentious issue in Thailand, often invoked in domestic politics. Similarly, Cambodia views the temple as a national heritage and sovereignty symbol. These sentiments have complicated diplomatic efforts and contributed to the protracted nature of the dispute.
WILL ICJ BE A SOLUTION NOW? WHY NOT ASEAN?
The enduring Thai-Cambodia border dispute, particularly surrounding the Preah Vihear Temple and nearby areas, reflects the limitations of regional diplomacy and the continuing relevance of international legal adjudication. Despite ASEAN’s past involvement, a definitive resolution to the dispute remains elusive—highlighting why Cambodia prefers the International Court of Justice (ICJ) as its platform of choice.
As a regional organization, ASEAN is founded on principles of consensus, non-interference, and mutual respect for sovereignty. These principles have allowed it to maintain harmony among diverse member states but also constrain its effectiveness in resolving complex territorial disputes. During the Preah Vihear tensions peak in 2008–2011, ASEAN attempted to mediate, propose ceasefires, and even offered observer missions. However, its diplomatic tools were non-binding, and efforts often stalled when met with resistance from either party, particularly from Thailand, which was reluctant to involve external actors in what it considered a bilateral matter. ASEAN’s lack of legal mechanisms and enforcement power ultimately left it unable to resolve the core issues.
In contrast, the ICJ provides a structured, rule-based framework for conflict resolution grounded in international law. Cambodia’s legal strategy has consistently favored the ICJ, evident in its successful appeal in 1962 and its request for interpretation in 2011. Cambodia values the clarity, neutrality, and binding nature of ICJ rulings. While not immune to political influence or delays in enforcement, ICJ decisions carry international legitimacy and moral weight. The court’s earlier rulings have already set legal precedents, which Cambodia sees as favorable to its case.
If both parties agree to submit to the ICJ’s jurisdiction again, the court could offer a lasting legal resolution that ASEAN’s consensus-based diplomacy cannot achieve. However, successful implementation still depends on the political will of both governments. Ultimately, the ICJ offers Cambodia the legal finality and global recognition it seeks, whereas ASEAN, for all its diplomatic value, remains a useful—but limited—conflict management tool. In deeply entrenched territorial disputes with historical, cultural, and political dimensions, binding legal adjudication remains the most viable path to a sustainable and peaceful resolution.
