Cambodia - Thailand : When Frozen Borders Fail: Why post-ceasefire fortification matters more than invasion rhetoric

Relayed on his Facebook accounts and via Cambodge Mag, this text dissects the December 2025 border shock between Phnom Penh and Bangkok. Far removed from semantic quarrels over an alleged “invasion,” Arnaud Darc warns of a deeper structural danger: unilateral post-ceasefire fortifications that erode the fragile legal balance governing border delimitation.

A Border Defined, but Not Delimited

Stretching over 803 kilometers, the land border between the two countries derives its course from the Franco-Siamese treaties of 1904 and 1907. Legally defined, it nevertheless remains imperfectly materialized, particularly in mountainous and forested areas.

The 2000 Memorandum of Understanding established the Joint Boundary Commission (JBC), imposing a freeze on claims: no unilateral change is permitted until joint surveys are completed.

This framework prevailed for more than twenty years, channeling an explosive dispute into a technical process—unlike the 2008–2011 clashes around Preah Vihear, ultimately settled by the International Court of Justice.

Arnaud Darc underscores this essential distinction—definition versus delimitation—which calls for patience rather than confrontation.

The December Escalation and Its Alarming Aftermath

On December 7, 2025, landmine explosions wounded Thai soldiers, triggering airstrikes (F-16s, T-50s), artillery fire, and ground incursions. The toll: 30 Cambodian civilians killed, 88 injured, and more than one million people displaced on both sides.

The bilateral ceasefire of December 27, endorsed by the 3rd Special General Border Commission (SGBC), sets out 16 points: cessation of hostilities, no troop reinforcement, a ban on new military construction, and the return of civilians.

The most serious developments came afterward.

In Chouk Chey, Banteay Meanchey province, opposite Ban Nong Chan, Bangkok deployed containers and barbed wire, blocking access for Cambodian civilians—AFP images dated January 2, 2026, corroborated by ASEAN observers. Phnom Penh denounced an “illegal occupation” on January 3; Bangkok invoked security concerns on what it claims is “its” contested soil.

Beyond the Word “Invasion”

The charge of “invasion,” echoed by Cambodian officials, rallies public opinion but collides with international law: proving a deliberate armed entry onto clearly sovereign territory is difficult in these gray zones under a freeze regime. Arnaud Darc cautions that this rhetorical outcry masks a far graver precedent—the normalization of post-conflict fortifications that violate the status quo and impose faits accomplis.

Prime Minister Hun Manet’s semantic shift—from “invasion” to “border dispute”—reflects a salutary pragmatism. It preserves credibility with ASEAN, donors, and judicial avenues, all of which favor tangible evidence over fiery declarations.

Gaps in the Agreements and Regional Echoes

The December 27 texts, extending those signed in Putrajaya (July 2025), prohibit advances or construction under the oversight of the ASEAN Observer Team (AOT) and bilateral units, without prejudice to the JBC.

Yet persistent ambiguities remain: no humanitarian corridors, no precise mapping of barriers, no timetable for returns to Chouk Chey; AOT reports lack public transparency.

This void enables a form of “strategic silence”: without gunfire, “preventive” encroachments take hold, trapping civilians. A breach here shakes the 2000 model, replacing surveyors with soldiers.

Toward Procedural De-Escalation?

Cambodia would benefit from meticulously documenting—via satellite imagery and geolocated testimony—these breaches of the status quo, framed as “illegal occupation” or “unauthorized presence.”

Bangkok must demonstrate the neutrality of its measures before the JBC and facilitate civilian return. ASEAN, through the AOT, should impose comprehensive reporting and JBC deadlines for priority segments (including demining), restoring the status quo ante before surveys resume.

Arnaud Darc concludes starkly: borders shift less through armed tidal waves than through the erosion of processes. “This border was meant to be the work of joint surveyors, ancestral markers, and patient talks—not of iron and fire.” Without a full revival of the JBC, the ordeal continues—and its true cost will surface in the next crisis.