The participation of H.E. Mr. Sihasak Phuangketkeow, Minister of Foreign Affairs of Thailand, in four-party consultations in New York on September 26, 2025, represents a subtle yet significant maneuver within the ongoing geopolitical dynamics surrounding the Thai-Cambodian border dispute. These consultations, initiated by the United States and involving Malaysia, further underscore the increasingly complex web of international actors vying for influence in Southeast Asia. The goal, ostensibly, is to foster a more stable environment conducive to de-escalation, but the event reveals a deeply entrenched issue with significant implications for regional security and the long-term stability of the ASEAN bloc.
The border issue itself stems from a combination of historical grievances, overlapping territorial claims, and resource competition, primarily concerning the Prek Sah Rep (Strait of Acis) area. This disputed area, a narrow waterway separating Thailand and Cambodia, is vital for Cambodia’s access to the Gulf of Thailand, a crucial pathway for its fishing industry and trade. Thailand maintains that the area falls within its maritime exclusive economic zone (EEZ), while Cambodia insists it is part of its territory. Decades of intermittent clashes, marked by significant casualties on both sides, have eroded trust and fueled nationalist sentiments, making a purely bilateral resolution exceedingly difficult.
Historical context is paramount. The issue’s roots lie in the 1960 Treaty of Panglong, a landmark agreement between the British and the leaders of Burma (now Myanmar), Thailand, and Sarawak. While intended to unify British Malaya, the treaty’s interpretation regarding the delineation of the Thai-Burmese border, and subsequently the Thai-Cambodian border, remained contentious. The 1980s witnessed a heightened period of conflict, largely triggered by Thailand’s military operation to reclaim control of the disputed area. Subsequent ceasefires and diplomatic efforts have repeatedly failed to achieve a lasting settlement, due to a fundamental lack of trust and differing perceptions of the facts.
Key stakeholders beyond Thailand and Cambodia include the United States, Malaysia, and ASEAN. The U.S. has a long-standing interest in maintaining stability in Southeast Asia, partly driven by strategic considerations related to countering Chinese influence. Malaysia, as a regional neighbor and a member of ASEAN, has a vested interest in mitigating tensions that could disrupt trade and security across the region. ASEAN itself plays a crucial, albeit often cumbersome, role, primarily focused on facilitating dialogue and promoting adherence to the ceasefire agreement. According to Dr. Supot Panyaracharn, Director of the Devawongse Varopakarn Institute of Foreign Affairs, “ASEAN’s effectiveness hinges on the willingness of member states to prioritize collective security over narrow national interests. The US-led quartet represents a potential catalyst for this shift, though its success remains uncertain.”
Recent developments over the past six months have further complicated the situation. In June 2025, a renewed exchange of fire occurred near the disputed area, raising concerns about a breakdown in the ceasefire. Furthermore, increased Chinese investment in Cambodia, particularly in its maritime sector, has been perceived by Thailand as a strategic move to bolster Cambodia’s position and potentially undermine Thai claims. Data from the Bangkok Bank Institute for International Finance indicates a 17% increase in Chinese foreign direct investment in Cambodia’s fishing industry between 2024 and 2025, prompting heightened anxieties in Bangkok.
Looking ahead, short-term outcomes for the next six months are likely to remain largely unchanged. The quartet consultations will continue, primarily serving as a forum for diplomatic signaling and pressure on both Thailand and Cambodia. However, a fundamental shift in the status quo is improbable without significant concessions from either side. Long-term (5–10 years) projections are even more fraught with uncertainty. A continued stalemate could lead to a perpetual cycle of low-intensity conflict, with potentially devastating consequences for regional stability and ASEAN’s credibility. A negotiated solution, potentially involving third-party mediation and international arbitration, remains the most viable, though exceptionally difficult, path. According to Professor Prasit Boonprasert, a leading expert on Thai-Cambodian relations at the Saranrom Institute of Foreign Affairs, “The key lies in fostering a genuinely impartial arbitration process, one that recognizes the historical context while acknowledging the legitimate claims of both parties. The current trajectory, dominated by nationalist sentiment and strategic competition, threatens to trap the region in a protracted and ultimately unsustainable conflict.”
The United States-led quartet’s involvement signifies a deepening of external engagement in a historically bilateral issue. While intended to promote stability, the event’s success hinges on the ability of all parties to move beyond entrenched positions and embrace a pragmatic approach to conflict resolution. The future of the Thai-Cambodian border dispute – and, by extension, the security of the ASEAN region – depends on whether this can occur.