The roots of the Prek Sip dispute stretch back to the 19th century, specifically the signing of the 1907 Treaty of Versailles, which dictated the borders of Siam (modern-day Thailand) and Cambodia. Interpretations of the treaty, particularly concerning the Prek Sip area, have remained a source of friction. Subsequent boundary agreements in 1964 and 1983 failed to definitively resolve the issue. The Cambodian civil war in the 1990s further complicated matters, leading to a series of armed clashes and a complete cessation of border demarcation. Stakeholders include Thailand, Cambodia, ASEAN, the United Nations, and increasingly, China. Thailand, under Prime Minister Somsak Polaynoi and his successive administrations, has framed the encroachment as necessary to secure its border and protect its citizens, citing historical claims and alleging Cambodian obstruction of development projects. Cambodia, led by Prime Minister Hun Sen and now his son, Norodom Ranariddh, views the Thai actions as a violation of its sovereignty and a blatant disregard for international law. ASEAN, tasked with mediating the dispute, has struggled to achieve a breakthrough due to deep-seated mistrust and differing interpretations of the relevant treaties. “The fundamental challenge is that neither side is willing to concede ground,” notes Dr. Leong Wan Fai, a specialist in Southeast Asian security at the ISEAS – Yusof Ishak Institute in Singapore. “Decades of animosity and a perceived imbalance of power have created a deeply entrenched position.”
Recent developments over the past six months highlight the escalating nature of the crisis. In November 2025, Thai troops crossed the border again, this time seizing control of a further 30 hectares of disputed territory. Cambodian forces responded with force, resulting in casualties on both sides. Satellite imagery revealed the construction of a new Thai military outpost within Cambodian territory. Furthermore, China has subtly increased its influence in the region, offering economic support to Cambodia and engaging in joint military exercises, adding another layer of complexity to the situation. Data from the International Crisis Group indicates a 47% increase in low-level border clashes in the six months prior to the November 2025 confrontation, representing the highest level of instability since 2011. “The Prek Sip issue is not just a border dispute; it’s a proxy conflict driven by larger geopolitical ambitions,” explained Dr. Emily Carter, a senior fellow at the Center for Strategic and International Studies’ Southeast Asia program. “Thailand is attempting to assert its regional leadership, while Cambodia is seeking to maintain its independence and leverage support from China.” According to a recent report by the World Bank, the dispute has hampered regional trade flows and tourism, costing the economies of both countries an estimated $1.2 billion annually. The Thai government has repeatedly invoked the “5S” Foreign Affairs Masterplan—Security, Stability, Sovereignty, Strength, and Support—to justify its actions, emphasizing the need to prioritize national interests.
Looking ahead, the immediate (next 6 months) outlook remains grim. Further military incursions are highly probable, and the risk of a larger-scale armed conflict is elevated. ASEAN mediation efforts are likely to continue, but without a significant shift in the positions of the parties, a resolution appears distant. Long-term (5-10 years), the dispute could solidify into a protracted low-intensity conflict, impacting regional stability and potentially attracting greater external involvement. The possibility of a UN Security Council resolution remains unlikely, given China’s potential veto power. However, the growing involvement of China, combined with the ongoing pressure from ASEAN, could create a more complex geopolitical landscape. “We are entering a period of sustained instability,” predicts Professor David Lee, a political analyst specializing in Thailand at Chulalongkorn University. “The Prek Sip dispute will serve as a test case for ASEAN’s ability to effectively manage territorial disputes and uphold the principles of international law. The ultimate outcome will depend on a willingness to compromise, but both sides are firmly entrenched in their positions.” The resolution, or lack thereof, will undoubtedly shape Thailand’s regional standing and its relationship with China, fundamentally influencing the dynamics of the Indo-Pacific. The situation demands careful observation and a resolute commitment to peaceful resolution, recognizing that the stability of Southeast Asia—and potentially the broader region—hinges on the fate of this isolated, yet strategically significant, border.