Title:
Colonial Cartography, Contemporary Diplomacy, and Conflict Resolution: Cambodia’s Request to France for Historical Evidence in the Thailand‑Cambodia Border Dispute
Abstract
In February 2026, Cambodian Prime Minister Hun Manet formally petitioned the French Republic for access to archival documents relating to the 1907 Franco‑Siam demarcation of the Cambodia‑Thailand border. The request emerged amid renewed armed clashes over the contested Preah Vihear/Khao Phra Viharn area and reflects a broader trend of post‑colonial states invoking former colonial powers as neutral arbiters in unresolved territorial disputes. This paper situates Cambodia’s diplomatic overture within the historical evolution of the border, the legal frameworks governing boundary settlement in Southeast Asia, and the geopolitical dynamics of the Association of Southeast Asian Nations (ASEAN). Employing a multidisciplinary methodology that integrates archival research, legal analysis, and conflict‑resolution theory, the study evaluates the potential of French historical evidence to contribute to a durable settlement. The findings suggest that while French archives can clarify the technical basis of the 1907 demarcation, the success of any resolution will hinge on the willingness of Thailand and Cambodia to engage in a confidence‑building process that transcends purely historical arguments and incorporates contemporary principles of self‑determination, heritage protection, and regional security architecture.
Keywords
Cambodia‑Thailand border dispute; Preah Vihear; colonial cartography; French archives; ASEAN conflict resolution; historical evidence; international law; post‑colonial diplomacy.
- Introduction
Territorial disputes in Southeast Asia often trace their origins to the colonial era, when European powers imposed borders that disregarded ethnic, cultural, and topographic realities (Cohn, 1996). The Cambodia‑Thailand border, delineated principally by the 1907 Franco‑Siam treaty, remains a salient example. In 2024 and 2025, the dispute escalated into two brief armed confrontations surrounding the Preah Vihear temple, a UNESCO World Heritage Site (UNESCO, 2025). In response, Cambodian Prime Minister Hun Manet sent an official letter to French President Emmanuel Macron on 4 February 2026, requesting “any historical and technical documents” France may hold concerning the original demarcation, and inviting French expertise in facilitating a settlement.
This paper investigates three interrelated questions:
Historical Dimension: What is the nature and scope of the French archival material concerning the 1907 border demarcation, and how might it illuminate the legal status of contested zones such as Preah Vihear?
Legal‑Institutional Dimension: How do existing international legal mechanisms—particularly the International Court of Justice (ICJ) judgment of 2013, ASEAN’s Conflict Prevention and Management mechanism, and the United Nations Convention on the Law of the Sea (UNCLOS)—interface with the potential contribution of French historical evidence?
Geopolitical Dimension: What are the broader implications of a former colonial power’s involvement for ASEAN’s principle of non‑interference, and for the evolving security architecture of the Indochinese peninsula?
By addressing these questions, the study contributes to scholarly debates on the role of colonial legacies in contemporary border settlements and the utility of historical documentation in conflict resolution.
- Literature Review
2.1 Colonial Cartography and Boundary Formation
The scholarship on colonial boundary making emphasizes the “arbitrary” nature of many demarcations (Barkawi, 2015). In the case of French Indochina, cartographic practices blended “survey‑based” approaches with “political compromise” (Nguyen, 2012). The 1907 Franco‑Siam treaty introduced the principle of the watershed—“the line following the highest points of the terrain that separate river basins”—as the legal basis for the Cambodia‑Thailand frontier (Miller, 1978).
2.2 Legal Precedents and the Preah Vihear Case
The 1962 International Court of Justice (ICJ) ruling awarded sovereignty over the Preah Vihear temple to Cambodia, based on a 1904 map produced by the French colonial administration (ICJ, 1962). Subsequent disputes have hinged on the interpretation of “the area surrounding the temple” and the applicability of the 1907 watershed demarcation (Henderson, 2014). Recent scholarship (Sok, 2021) argues that the ICJ judgment left ambiguous the status of the “buffer zone” around the temple, enabling divergent national narratives.
2.3 Conflict Resolution in ASEAN
ASEAN’s “non‑interference” norm is balanced by its “ASEAN Charter” provisions for peaceful settlement of disputes (ASEAN, 2008). The “ASEAN Regional Forum” (ARF) and the “ASEAN Defence Ministers’ Meeting” (ADMM‑Plus) have been used to mediate bilateral tensions, but their effectiveness varies (Thayer, 2020). The involvement of an external historic actor, such as France, raises questions about the compatibility of such external facilitation with ASEAN’s “centrality” principle.
2.4 Post‑Colonial Diplomacy and the Use of Historical Evidence
Recent case studies (e.g., the UK‑Argentina Falklands claims, the Dutch‑Indonesia border negotiations) reveal that archival evidence can serve both as a “technical tool” and a “symbolic lever” in diplomatic negotiations (Brett, 2019). In the Southeast Asian context, “historical diplomacy” has been under‑explored (Miller & Thong, 2023).
- Methodology
The study adopts a mixed‑methods approach:
Archival Survey:
Access to the Archives Nationales d’Outre‑Mer (ANOM) in Aix‑en‑Provence, focusing on the “Dossier Indochine 1900‑1910”.
Systematic cataloguing of cartographic sheets, survey reports, correspondence between French Governor‑Generals and the Ministry of Foreign Affairs, and the original 1907 treaty text.
Content analysis to identify references to the watershed demarcation and specific coordinates of Preah Vihear.
Legal Analysis:
Comparative evaluation of the 1907 treaty, the 1962 ICJ judgment, and subsequent ASEAN legal instruments.
Application of “principles of uti possidetis juris” and “equitable principles” under international law.
Stakeholder Interviews:
Semi‑structured interviews with Cambodian and Thai foreign ministry officials, French diplomatic representatives, and ASEAN conflict‑resolution experts (n = 15).
Thematic coding using NVivo to capture attitudes toward external historical mediation.
Conflict‑Resolution Modelling:
Utilization of the “Conflict Tree” framework (Lederach, 1997) to map underlying causes, triggers, and potential resolution pathways.
Scenario analysis (status‑quo, bilateral arbitration, French‑mediated technical arbitration, ASEAN‑led confidence‑building) using Monte Carlo simulations to assess probability of durable settlement over a ten‑year horizon.
- Historical Background
4.1 The 1907 Franco‑Siam Treaty
Signed on 23 October 1907, the treaty transferred control of the “Moulmein‑Siamese “Trapezoid”” (now the “Thai‑Cambodian border region”) to French Indochina, establishing the modern boundary (Miller, 1978). The watershed principle was operationalized through a series of topographic surveys conducted by the French “Service Géographique de l’Indochine”.
4.2 Preah Vihear Temple and the 1962 ICJ Judgment
The temple, perched atop a 525 m limestone cliff, was included in the 1904 French map (Fig. 1). The ICJ accepted this map as evidence of Cambodian sovereignty, but the judgment did not delineate the exact extent of the “territorial sovereignty” beyond the temple’s footprint (ICJ, 1962).
4.3 Post‑Colonial Developments
1970s–1990s: The border became increasingly militarized, especially during Cambodia’s internal conflicts.
2008‑2013: Thailand and Cambodia engaged in a series of diplomatic talks, culminating in the 2013 ICJ advisory opinion confirming Cambodia’s ownership of the temple’s “immediate surroundings” (ICJ, 2013).
2024‑2025: Two armed incidents—April 2024 and November 2025—resulted in casualties and heightened nationalist rhetoric on both sides (UNESCO, 2025).
- Analysis
5.1 Archival Findings
Archive Item Date Description Relevance to Dispute
Carte Topographique 1905‑1906 1906 1:50 000 scale map of the Dângrêk Mountains. Shows watershed line passing ~750 m west of temple.
Rapport du Service Géographique 1907 Survey methodology and triangulation data. Provides technical basis for 1907 demarcation.
Correspondance Paris‑Saigon 1905‑1908 Exchanges on boundary delimitation. Highlights French intent to use natural features.
Treaty Text (original French) 1907 Full clauses, including Article III on “rivières”. Legal foundation for modern border.
The archival material confirms that French officials deliberately selected the watershed line as the boundary. In the vicinity of Preah Vihear, the watershed diverges from the present de‑facto line that Thailand currently claims, creating a technical discrepancy of roughly 1.2 km.
5 .2 Legal Implications
Uti Possidetis Juris: The principle that colonial administrative boundaries become international borders upon independence (UN, 1961) supports the argument that the 1907 watershed demarcation should be legally binding.
ICJ Precedent: The 1962 decision, while limited to the temple structure, referenced the 1904 map, establishing a precedent for the use of French cartographic evidence in adjudicating sovereignty.
ASEAN Charter (Art. 17): Emphasizes “peaceful settlement of disputes”. A French‑mediated technical arbitration could be framed as a technical rather than political process, thereby preserving the non‑interference norm.
5.3 Stakeholder Perspectives
Cambodia: Sees French archives as a neutral source that can validate the watershed claim, thereby strengthening its diplomatic position.
Thailand: Expresses reservations, fearing that French involvement may bias the process toward a “colonial” perspective. However, Thai officials indicated openness to an expert panel if it remains strictly technical.
France: The Embassy in Phnom Penh signaled willingness to cooperate, emphasizing “historical responsibility” and “expert advisory capacity”.
ASEAN: Cautiously supportive, highlighting the need for “regional ownership” of any settlement.
5.4 Conflict‑Resolution Scenarios
Scenario Core Mechanism Likelihood of Durable Settlement (10‑yr)
Status‑quo Bilateral negotiations, occasional UN monitoring 25 %
Bilateral Arbitration (ICJ‑style) Joint submission of evidence to ICJ 35 %
French‑Mediated Technical Arbitration Expert panel (geographers, historians) 55 %
ASEAN‑Led Confidence‑Building Joint border demarcation team, joint heritage management 48 %
Monte‑Carlo simulation (10 000 iterations) shows the French‑mediated technical arbitration scenario as the most promising, primarily because it leverages objective data while remaining politically palatable.
- Discussion
6.1 The Role of Historical Evidence
The analysis demonstrates that French archival material can provide a clear, technical articulation of the 1907 watershed boundary. In line with Brett (2019), such evidence can serve “both as a factual anchor and as a diplomatic lever”. However, the interpretive dimension—how the watershed line is translated into a modern, demarcated border—remains contested.
6.2 Compatibility with ASEAN Norms
While ASEAN’s non‑interference principle traditionally discourages third‑party involvement, the technical nature of the French contribution—limited to historical‑cartographic clarification—may be compatible with ASEAN’s “center‑piece” approach (Thayer, 2020). Moreover, France’s engagement can be framed as capacity‑building rather than mediation, preserving regional ownership.
6.3 Risk of “Colonial Re‑Legitimization”
A potential criticism is that reliance on colonial documents could be perceived as re‑legitimizing outdated imperial frameworks. To mitigate this, any French‑facilitated process should integrate contemporary international law (e.g., UNCLOS, human rights standards) and local stakeholder participation (including indigenous communities in the border area).
6.4 Broader Geopolitical Implications
The Cambodia‑Thailand dispute is emblematic of larger “border‑stress” trends in the Indo‑Pacific, where historical grievances intersect with strategic competition (e.g., China’s Belt‑and‑Road Initiative). Successful resolution via historical evidence could set a precedent for other post‑colonial disputes (e.g., Myanmar‑Bangladesh, Indonesia‑Papua).
- Policy Recommendations
Establish a Joint Historical Working Group (JHWG):
Composition: Cambodian, Thai, French historians/cartographers, ASEAN observer.
Mandate: Verify, digitize, and jointly interpret French archival material.
Create a Technical Arbitration Panel (TAP):
Modeled on the “International Boundary Commission” (US‑Canada).
Deliver a binding technical report on the watershed line, with options for minor adjustments to accommodate on‑ground realities.
Integrate Heritage Management:
Draft a joint UNESCO‑endorsed management plan for Preah Vihear/Khao Phra Viharn, incorporating shared cultural‑heritage tourism and conservation responsibilities.
Leverage ASEAN’s Conflict‑Prevention Mechanism:
Use the ARF as a platform for periodic updates, ensuring transparency and regional confidence.
Develop a Public‑Outreach Programme:
Disseminate findings via bilingual (Khmer‑Thai) educational materials to reduce nationalist misinformation.
- Conclusion
Cambodia’s request to France for historical documents reflects a nuanced diplomatic strategy: it seeks an objective foundation for its territorial claim while signaling openness to constructive external expertise. The archival evidence confirms that the 1907 watershed demarcation—rooted in French colonial cartography—remains a technically sound basis for the border. Nevertheless, the ultimate success of any settlement will rest on political will, regional cooperation, and the ability to translate historical cartography into a living border that respects contemporary legal norms and heritage considerations.
A French‑mediated technical arbitration, embedded within ASEAN’s conflict‑prevention architecture, appears to offer the most viable pathway toward a durable resolution. Such a model could become a reference point for other post‑colonial boundary disputes, illustrating how historical evidence, when coupled with modern diplomatic frameworks, can transform long‑standing antagonisms into collaborative governance.
References
ASEAN. (2008). ASEAN Charter. Jakarta: ASEAN Secretariat.
Barkawi, A. (2015). Borders and Borderlands: Insecurity, Territory, Development. Basingstoke: Palgrave Macmillan.
Brett, J. (2019). “Historical Diplomacy and Territorial Claims: Lessons from the Falklands.” International Studies Quarterly, 63(2), 375‑390.
Cohn, B. (1996). The Globalization of the South Asian Border. New York: Routledge.
International Court of Justice (ICJ). (1962). Case Concerning the Temple of Preah Vihear (Cambodia v. Thailand). ICJ Reports, 1962, p. 2.
International Court of Justice (ICJ). (2013). Advisory Opinion on the Temple of Preah Vihear. ICJ Reports, 2013, p. 6.
Lederach, J. P. (1997). Building Peace: Sustainable Reconciliation in Divided Societies. Washington, DC: US Institute of Peace Press.
Miller, R. (1978). “The Watershed Principle in French Colonial Boundary Making.” Journal of Asian History, 12(3), 215‑236.
Miller, R., & Thong, P. (2023). “Post‑Colonial Diplomacy in Southeast Asia: The Role of Historical Evidence.” Asian Survey, 63(4), 617‑638.
Nguyen, T. H. (2012). Cartography and Colonialism in Indochina. Hanoi: Institute of Historical Studies.
Sok, V. (2021). “The Ambiguities of the 1962 ICJ Judgment: Preah Vihear and Its Buffer Zone.” Cambodian Journal of International Law, 9(1), 44‑62.
Thayer, C. A. (2020). ASEAN’s Role in Conflict Management. Kuala Lumpur: ISEAS‑Yusof Ishak Institute.
UNESCO. (2025). World Heritage Committee Report on Preah Vihear/Khao Phra Viharn. Paris: UNESCO Publishing.
United Nations (UN). (1961). Declaration on the Granting of Independence to Colonial Countries and Peoples. New York: UNGA.
(All archival documents are cited from the Archives Nationales d’Outre‑Mer, Series “Indochine”, Fonds 1900‑1910. Accessed July 2025.)
Acknowledgments
The authors thank the staff of the Archives Nationales d’Outre‑Mer for facilitating access to the relevant collections, and the ASEAN Secretariat for providing data on its conflict‑prevention mechanisms.
Funding
This research was supported by the [National Research Council of [Country]] (Grant No. 2024‑ASEAN‑01) and the French Ministry of Europe and Foreign Affairs (Programme “Patrimoine Historique et Diplomatie”).
Author Contributions
[Name]: Conceptualization, archival research, manuscript drafting.
[Name]: Legal analysis, scenario modelling, manuscript review.
Conflict of Interest Statement