There has been a dramatic escalation in a long-running border conflict between Thailand and Cambodia. On July 23, five Thai soldiers from a border patrol unit in Ubon Ratchathani province were seriously injured after stepping on a land mine – a second such incident in a week. This prompted the Thai government to expel Cambodia’s ambassador from the country and recall its own ambassador from Cambodia. The following morning, Cambodia retaliated by expelling the Thai ambassador and recalling its embassy staff from Bangkok. Both sides have exchanged increasingly lethal fire.Cambodia has fired rockets and artillery across the Thai border into several provinces, killing at least 11 civilians and one soldier. Thailand launched air strikes at Cambodia in return, reportedly targeting military bases in the disputed area around the Preah Vihear Hindu temple. Verified information is currently scarce as both sides are blaming each other for starting the fight.The current flare-up started in late May, when a Cambodian soldier was killed in a exchange of fire between the two armies. But the roots of the conflict date back to the colonial era in the 19th and early 20th centuries. Before European powers expanded their colonial interests to south-east Asia, the concept of a bordered nation-state was alien to local rulers. Life in pre-colonial south-east Asia was organised into loosely structured polities that had no clear boundaries.There were several larger cities, which served as important centres of power and trade, and many smaller towns and villages that maintained relations with these cities. The further these towns and villages were from the cities, the less control and influence the cities had over them.The British and French introduced the concept of nations with borders to mainland south-east Asia, drawing the first official maps of Thailand (then known as Siam) and Cambodia. In the case of Thailand, the only south-east Asian nation never to be formally colonised, the mapping was also done at the request of the Siamese kings. Thailand’s current borders were shaped by several different maps and treaties that followed the 1893 Paknam incident, during which two French gunboats sailed up the Chao Praya River and blockaded Bangkok. To preserve its sovereignty as an emerging nation, Siam ceded considerable territorial claims to France after this incident. This included several provinces in present-day Cambodia, which are home to ancient temples. A 1907 map drawn by the French defined these territories, although with a considerable degree of vagueness. The map became a sore point in Cambodia-Thai relations following Cambodia’s independence in 1953, especially in regard to disputes over the Preah Vihear temple.Preah Vihear templeFollowing France’s withdrawal from south-east Asia in 1954, Thailand occupied Preah Vihear. Cambodia raised the issue of Thai occupation with the International Court of Justice (ICJ), which ruled in 1962 that the temple belonged to Cambodia based on the French map. Thailand reluctantly accepted the ruling, but continued to dispute the area surrounding the temple. The conflict flared up again in 2008 when the UN world heritage body Unesco awarded the temple world heritage status. Cambodia’s application initially received support from the then new Thai government of prime minister Samak Sundaravej, a close ally of the recently ousted Thaksin Shinawatra. Anti-Thaksin groups used the government’s support to drive an ultra-nationalist campaign against the Samak government. This eventually contributed to large-scale domestic political protests that saw Samak’s government and that of his successor, Somchai Wongsawat, both ousted from power in 2008 in a series of judicial coups.The period from 2008 to 2011 was marked by high tensions between the two countries, with sporadic armed clashes between their respective armies in the areas surrounding the temple. The newly appointed Thai government of Abhisit Vejjajiva was sympathetic towards the ultra-nationalist anti-Thaksin groups. So there was no de-escalation of the conflict from the Thai side. Hun Sen, who was then Cambodia’s prime minister, also benefited from the conflict as it helped buttress his nationalist credentials.But a particularly violent round of armed clashes followed in February 2011, resulting in at least eight civilian fatalities, 20 injured soldiers and many displaced civilians on both sides. Hun Sen then raised the issue of Cambodian sovereignty over the temple and its surrounding area with the ICJ. The ICJ issued a provisional ruling favouring Cambodia and ordered both sides to withdraw military personnel from the area. Despite the initial refusal of Thai troops to leave, the two countries agreed to withdraw their forces in December 2011.The final ICJ ruling came in late 2013, again affirming Cambodia’s sovereignty of the area. It coincided with another period of domestic political instability in Thailand. The government of Yingluck Shinawatra, Thaksin’s younger sister, was facing mass public protests from anti-Thaksin groups. While the ruling did not play a decisive role in the eventual downfall of her government, it added fuel to the already explosive political environment. The border conflict went largely dormant after the 2013 ICJ ruling, until the new round of clashes broke out in May 2025. Thai and Cambodian troops have periodically clashed in the area surrounding the Preah Vihear temple. Kim Za / Shutterstock Given the history of tensions and armed disputes over territory between Cambodia and Thailand, the recent escalation is not without precedent. What is new, though, is that this round is as much between two countries as it is between two ruling families. Over the past 20 years, a close personal relationship formed between Hun Sen and Thaksin. But this relationship unravelled when Hun Sen, who remains a hugely influential figure in Cambodian politics, released a private audio recording of his call with Thaksin’s daughter, Paetongtarn. The leak put her premiership on the line. Paetongtarn has since been suspended from office pending a court ruling, with Cambodia-Thai relations reaching new lows. Given the intermixing of personal animosities, a quick diplomatic resolution to the escalating conflict seems unlikely. Read more: A border conflict may cost the Thai prime minister her job Get your news from actual experts, straight to your inbox. Sign up to our daily newsletter to receive all The Conversation UK’s latest coverage of news and research, from politics and business to the arts and sciences.Petra Alderman does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.