Why Peace Keeps Failing on the Cambodia–Thailand Border |
Hostilities between Cambodia and Thailand flared into open conflict in July 2025, as firefights erupted across multiple points of their shared border. For a brief moment, Cambodians and Thais allowed themselves to believe the worst might be ending when the United States intervened, first to mediate a ceasefire on July 28 that ended the fighting. Working alongside ASEAN and the Malaysian government, President Donald Trump then helped broker the Kuala Lumpur Peace Accord, which was signed on October 26 during the 47th ASEAN Summit in Malaysia. Presented as a joint declaration by the prime ministers of both countries, the accord reaffirmed the cessation of hostilities and sought to turn the fragile July ceasefire into a workable, long-term framework for de-escalation. Cambodia and Thailand agreed to a phased withdrawal of heavy weaponry from the most volatile stretches of the frontier, with Trump and Malaysian Prime Minister Anwar Ibrahim serving as witnesses.
But the accord never attempted to confront the territorial dispute at the center of the conflict – a dispute that is now more than 100 years old. In retrospect, a return to conflict was probably inevitable.
In early November, several Thai soldiers were injured by a landmine near the border, an incident that Bangkok claimed stemmed from newly planted Cambodian mines. Thailand responded by suspending its obligations under the October 26 peace deal. Phnom Penh denied laying new mines, insisting the explosives were remnants of earlier conflicts. Tensions nonetheless intensified. After an incident on December 7, the two sides soon exchanged heavy fire once again, displacing more than 750,000 people and effectively rendering the peace framework defunct.
Colonial Origins
To trace the origins of the conflict, one must return to the period when Cambodia was still part of French Indochina. In the early twentieth century, Siam (modern-day Thailand) was struggling to preserve what remained of its independence and territorial integrity, while France sought to consolidate and secure the borders of its colonial possessions in Cambodia and Laos. These competing imperatives led the two sides to negotiate a new boundary arrangement, culminating in a treaty signed in Paris on February 13, 1904. Its stated aim was to demarcate the frontier and resolve contested areas, including in the Dangrek Mountains.
The treaty adopted the watershed principle as the basis for the boundary: the crest of the mountain range, where water flows in opposite directions, would serve as the natural dividing line. However, the treaty left much of the actual implementation, including detailed surveying and the production of official maps, to a Franco-Siamese boundary commission. It was this delegation that eventually sowed the seeds of the modern controversy.
The mixed boundary commission operated between roughly 1905 and 1907. Although formally a joint body, much of the surveying and cartographic work was carried out on the ground by French technical officers. The commission ultimately produced a series of maps depicting the frontier between Siam and French Indochina.
In 1907, France and Siam entered into a second treaty that adjusted other sections of the frontier: Battambang, Siem Reap, and Sisophon were returned to Cambodia, while Trat, which France had been granted in the 1904 treaty, was retroceded to Siam. Above all, this treaty cemented the authority and finality of the boundary-making process conducted by the commission, which had completed its fieldwork and was moving toward the technical stages of drafting and printing the maps.
One of these maps was later known as the