Cambodia–Thailand border in the context of 2025 Cambodia–Thailand border conflict

The Fall of Phnom Penh was the capture of Phnom Penh, capital of the Khmer Republic (in present-day Cambodia), by the Khmer Rouge on 17 April 1975, effectively ending the Cambodian Civil War. At the beginning of the month, Phnom Penh, one of the last remaining strongholds of the Khmer Republic, was surrounded by the Khmer Rouge and totally dependent on aerial resupply through Pochentong Airport.

With a Khmer Rouge victory imminent, the United States government evacuated US nationals and allied Cambodians on 12 April. On 17 April, the Khmer Republic government evacuated the city, intending to establish a new government center close to the Thai border to continue resistance. Later that day, the last defences around Phnom Penh were overrun and the Khmer Rouge occupied Phnom Penh.

The Cambodia–Thailand border dispute is a territorial dispute between Cambodia and Thailand over certain areas of their border. It began in the 1950s, shortly after Cambodia's independence from France, and first centred on ownership of the Preah Vihear temple. The case was brought to the International Court of Justice (ICJ), who decided in 1962 in favour of Cambodia. The issue became dormant over the following decades as Cambodia fell into civil war, but remained unresolved as sections of the countries' borders were never jointly demarcated. The dispute erupted into open conflict in 2008, following Cambodia's nomination of the temple as a UNESCO World Heritage Site and Thai protesters pushing their government over the issue. The clashes led to a request for interpretation from the ICJ to clarify the 1962 ruling, which was decided in 2013. During this round of conflict, disputes also arose over other overlapping border areas, including those around the ancient Khmer temples of Prasat Ta Muen Thom and Prasat Ta Krabey. The conflict subsided for over a decade until it erupted again in 2025, with the worst fighting since the dispute began.

The dispute mostly stems from the Franco-Siamese treaties of 1904 and 1907, which defined the final boundary between Siam (as Thailand was then known) and French Indochina, the borders of which were inherited by Cambodia. While the treaty defined the relevant segment of the boundary along the watershed line of the Dangrek Mountains, demarcation of the border by French surveyors produced maps that deviated from the line in the now-disputed areas, including around the Preah Vihear temple. While Thailand argued at the ICJ that it never approved the maps and that the temple's location on a cliff, more accessible from the Thai side, indicated that it was on Thai territory, the ICJ decided in favour of Cambodia largely based on the fact that Siam never officially protested the map or claimed ownership of the temple while it was under French control. Cambodia also views itself as having rightful claims to the temples due to closer cultural affinity as successor to the Khmer Empire.

The territorial dispute between Cambodia and Thailand escalated into a direct armed confrontation on 24 July 2025 along the Cambodia–Thailand border. Although both governments subsequently agreed to an unconditional ceasefire on 28 July 2025, hostilities later resumed in December, during which Thai forces seized several towns and strategic hills in contested areas near the frontier.

Tensions had sharply increased on 23 July, when a Thai soldier was seriously injured after stepping on a PMN-2 anti-personnel landmine in Nam Yuen district, Ubon Ratchathani province. The incident served as the immediate trigger for wider hostilities. On the following day, direct armed clashes erupted across multiple sectors of the border. Thai media widely reported that Cambodia's BM-21 multiple rocket launchers, which struck Thai residential neighbourhoods, a hospital, and a gas station, acted as the catalyst for the outbreak of full-scale fighting on 24 July 2025. Both sides asserted that their actions were taken in self-defence and accused the other of initiating the conflict. The clashes resulted in the displacement of more than 200,000 civilians across northeastern Thailand and northern Cambodia.