When Neighbours Become Enemies

Thailand and Cambodia are engaged in their worst border conflict in decades. Since July, the conflict has killed dozens, displaced lakhs, and shattered a peace deal signed just weeks earlier.

The Thailand-Cambodia border disagreement dates back to 1907, when France, which ruled Cambodia at the time, signed a treaty with Siam (now Thailand) to establish their shared border. The treaty stated that the border would follow the watershed of the Dangrek Mountains. While this seemed straightforward, French maps placed several ancient temples and pockets of land inside Cambodia, even though the watershed would have put them in Thai territory.

These were not minor disputes. One contested area includes the 11th-century Preah Vihear temple, which sits on the border. In 1962, the International Court of Justice ruled it belonged to Cambodia, but the wider boundary issue remained unresolved. With no agreed border line, the dispute simmered for decades, with occasional but contained clashes.

Then in 2025, the situation began to deteriorate rapidly.

When Fighting Began

On May 28, a Cambodian soldier was killed near the border, prompting Cambodia to ban Thai imports and Thailand to close crossings. By July 24, the dispute had escalated into open warfare, with both sides deploying heavy weapons and civilians fleeing border areas or sheltering in schools and temples.

The Leaked Call

A month earlier, a private phone call between Thailand’s then Prime Minister Paetongtarn Shinawatra and Cambodia’s former leader Hun Sen surfaced in June, triggering a political crisis that reshaped Thai politics.

In the call, Paetongtarn addressed Hun Sen informally, calling him “uncle”, while appearing to criticise Thailand’s military and seek his advice on domestic matters—fuelling claims of undue foreign influence.

Hun Sen later released the recording after relations soured, triggering nationalist outrage and mass protests in Thailand. The fallout proved catastrophic for Paetongtarn’s government: in August 2025, the Constitutional Court removed her from office, reshaping the country’s political trajectory.

Short-Lived Peace

On July 28, just four days after fighting erupted, a Malaysia-brokered ceasefire saw both sides pull back and halt fire. The agreement appeared to hold, keeping the border largely quiet for two months.

In October, a more formal peace deal—the Kuala Lumpur Peace Accords—was signed at an ASEAN summit in Malaysia. It called for withdrawing heavy weapons, deploying ASEAN observers, clearing landmines jointly, and restoring diplomatic ties, with US President Trump attending the signing. But the peace was short-lived.

The Collapse

On November 10, Thai soldiers were injured in a landmine blast, prompting Thailand to accuse Cambodia of planting new mines during the ceasefire—a claim Cambodia denied, saying the area remains contaminated by unexploded ordnance from past conflicts and that Thai troops may have entered known minefields.

On December 7, Thailand reported another ambush on its military engineers and responded with heavy airstrikes on Cambodian positions, which Cambodia said were unprovoked. Fighting quickly spread across multiple border points, leaving at least 52 dead and over 750,000 displaced by December 18.Who's Trying to Fix This?

Multiple countries and organisations are attempting to mediate the conflict because instability in Southeast Asia affects everyone.

Malaysia, as the ASEAN chair, has led mediation and deployed an ASEAN observer team to monitor the border. The United States also stepped in, seeking to counter China’s regional influence and prevent wider instability. China, meanwhile, has positioned itself as a mediator, sending a special envoy amid concerns over arms supplies to both sides and major economic projects threatened by conflict.

What Happens Next

Currently, there is no immediate end to the conflict. Thailand's military leadership has stated that it will not accept a ceasefire until Cambodia demonstrates a genuine commitment to border security and stops what Thailand views as provocative behaviour. Cambodia insists that Thailand is the aggressor and must cease military operations first.

The most likely scenarios are (1) the fighting gradually de-escalates as both countries recognise the costs are unsustainable; (2) one side achieves military objectives and then agrees to a negotiated settlement; or (3) a new mediated agreement emerges that, like the October accord, temporarily stops fighting but doesn't resolve the underlying territorial dispute.

None of these options provides a permanent solution to the border dispute. As long as Thailand and Cambodia disagree on where their border actually is, as long as both countries face domestic political incentives to maintain nationalist positions, and as long as external powers compete to mediate rather than allowing regional resolution, border conflict remains possible.

(The writer is a foreign affairs expert. Views personal.)