Thailand–Cambodia

What it is

Thailand and Cambodia share an approximately 817-kilometer border fixed by French colonial-era treaties of 1904 and 1907 but never jointly demarcated in full. The disputed zone concentrates along the Dangrek Mountains escarpment in the northeast and the Cardamom Mountains in the southwest, with the most contested ground centered on two ancient Khmer temple complexes: Preah Vihear, on the Dangrek cliff-line, and Ta Muen Thom. Because the 1904 treaty specified a watershed line while French survey maps deviated from that line in places, the two countries have disagreed about where sovereignty runs for over a century. The bilateral relationship combines unresolved colonial cartography, domestic political incentives that reward nationalist escalation, and ASEAN's structural inability to enforce bilateral agreements between its own member states.

History

After Cambodia gained independence in 1954, Thailand occupied the Preah Vihear temple complex. Cambodia brought the case to the International Court of Justice; on 15 June 1962 the court ruled in Cambodia's favor, finding that Siam had accepted the French survey maps by decades of non-protest, and ordered Thailand to withdraw military and police forces and return removed objects. Thailand complied with withdrawal but never fully accepted the underlying cartography.

The dispute lay dormant through Cambodia's civil war years. UNESCO's 2008 inscription of Preah Vihear as a World Heritage Site revived it, triggering armed clashes along the border that killed at least 19 soldiers by 2011. Cambodia filed in April 2011 for ICJ interpretation of the 1962 judgment, arguing Thailand acknowledged Cambodian sovereignty over the temple building but not its surrounding promontory. The court's November 2013 ruling extended Cambodian sovereignty to the entire promontory, not just the temple structure, ordering complete Thai military withdrawal. Thailand accepted the ruling while contesting parts of it.

Current state

The 2025 armed conflict was the most serious bilateral confrontation in decades. A skirmish in May 2025 near Preah Vihear killed a Cambodian soldier, triggering a cycle of trade bans and border closures. On 24 July 2025, fighting broke out simultaneously across 12 border sites; the Royal Thai Air Force deployed F-16s in combat operations for the first time since the 1987-88 Thai-Laotian border war. Five days of fighting displaced over 140,000 civilians and froze an estimated US$5 billion in cross-border trade. Malaysia, as ASEAN Chair in 2025, brokered a ceasefire on 28 July.

The July truce held uneasily until December. Thailand launched fresh air strikes on 8 December, followed by "Operation Sattawat" on 10 December, in which Royal Thai Army units seized localities in northern Cambodia. Cambodia reported at least 30 civilian deaths; Thailand acknowledged 26 soldiers killed. A second ceasefire took effect on 27 December 2025. The December 2025 truce holds narrowly as of July 2026: all border crossings remain shut, both governments trade ceasefire-violation accusations, and Joint Boundary Commission demarcation talks are deadlocked. Cambodia demands Thailand set a JBC meeting date; Thailand conditions any meeting on de-escalation and verified landmine-clearing. The United States pledged US$45 million in January 2026 to support the truce.

Relationships

Cambodia under Prime Minister Hun Manet, who succeeded his father Hun Sen in August 2023, used the 2025 conflict to consolidate domestic authority. Thailand's position was complicated by internal political instability: Prime Minister Paetongtarn Shinawatra was suspended and removed from office after a leaked phone call with Hun Sen became public during the July 2025 crisis, a sequence nationalist constituencies in Thailand exploited. For context on Thailand's political realignment following the crisis, see Anutin's Bhumjaithai wins Thailand's snap vote as voters back a new charter. The dispute strains ASEAN's consensus architecture; the bloc brokered both ceasefires through Malaysian shuttle diplomacy but cannot compel demarcation or the reopening of border crossings.

What to watch

• Whether Thailand's government sets a Joint Boundary Commission date that allows demarcation around Preah Vihear and Ta Muen Thom to resume.
• Reopening of any border crossing as a concrete confidence-building measure, given all remain closed as of July 2026.
• Any military incident along the Dangrek line that collapses the December 2025 truce.
• Whether either government returns to the ICJ if bilateral diplomacy cannot resolve the promontory boundaries.