Why are Thailand and Cambodia fighting?

On Dec. 27, defense ministers from Cambodia and Thailand signed a ceasefire deal to end months of fighting. Two days later, the countries’ foreign ministers met in China for talks to end the century-long conflict. The most recent crisis began in May when a Cambodian soldier died following a skirmish. That prompted both countries to impose trade restrictions and reinforce troop deployments. Fighting intensified again in July and escalated in early December. Since then, at least 48 people, including both troops and civilians, have been killed, although official accounts vary. More than 500,000 civilians have been displaced, leading to the expansion of refugee camps and the closure of schools, hospitals, and other critical infrastructure.

What started the dispute? The conflict between Thailand and Cambodia stems from a long-standing territorial dispute rooted in colonial-era border mapping along their roughly 500-mile frontier. The dispute originated in a 1907 colonial map drawn when Cambodia was a French protectorate and Thailand, then Siam, remained independent. In defining the boundary, French cartographers introduced ambiguities that remain flash points for repeated border clashes.

What kind of ambiguities? The most sensitive points involve disputed temple sites, particularly the Preah Vihear area and the Temple of Ta Muen Thom. In 1962, the International Court of Justice (ICJ) ruled that the Preah Vihear temple belonged to Cambodia but left the surrounding land undefined.

What happened during Cambodia’s civil war? After the 1962 ruling, the formal border dispute faded from view as Cambodia descended into civil war in the late 1960s and 1970s, culminating in the brutal Khmer Rouge regime that killed roughly a quarter of the country’s population. From 1975 to 1989, the frontier became a lawless zone of guerrilla activity after Khmer Rouge forces fled toward the Thai border following Vietnam’s 1979 invasion of Cambodia.

Throughout the 1980s, Vietnamese troops repeatedly crossed into Thai territory while pursuing Khmer Rouge fighters, triggering frequent clashes with Thai forces that included artillery exchanges, tank battles, and Thai airstrikes. By 1981, more than 250,000 Cambodian and Vietnamese refugees lived in camps along the border. Relative calm returned only after Vietnam’s withdrawal in 1989 and the signing of the Paris Peace Accords in 1991.

How did things get so heated again? The dispute resurfaced in 2008 when Cambodia sought UNESCO World Heritage status for the 11th-century Preah Vihear temple without Thai consent. That ignited intense nationalist backlash in Thailand, where opposition politicians and nationalist groups accused the government of betraying national interests. The controversy contributed to the fall of Prime Minister Samak Sundaravej’s government and strengthened the influence of Thailand’s military and ultraroyalist factions, who framed border defense as central to national sovereignty. Military clashes followed, killing dozens and displacing thousands.

A 2011 ICJ clarification reaffirmed Cambodian ownership of the temple but again failed to resolve adjacent territorial claims, enabling both governments to justify continued military deployments. Since then, nationalist sentiment on both sides has made compromise politically toxic, with sporadic clashes killing soldiers and civilians in recurring cycles of escalation.