State of Peace and Conflict 2025

CWA # 1899
State of Peace and Conflict 2025
Thailand and Cambodia: Border Clashes, Fragile ceasefire and Recurring conflict
Conflict Weekly #313, 31 December 2025, Vol. 6, No. 52

R Preetha
31 December 2025

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What happened?
Border tensions that started in May 2025 flared up again in December, despite a US-brokered ceasefire. This year (2025) witnessed the second major flare-up between Thailand and Cambodia after 2008. 

In May, tensions between the two countries escalated when a Cambodian soldier was killed in a skirmish, leading to troop buildups and diplomatic strains. In July, five days of intense fighting involving artillery, rockets, and Thai airstrikes killed at least 48 people and displaced over 300,000. A ceasefire was brokered through US pressure and Malaysian mediation, ending the tensions.

In October, a ceasefire agreement was signed in Kuala Lumpur, including troop withdrawals and de-mining. However, in November, Thailand suspended its implementation after a landmine injured a soldier, accusing Cambodia of planting new mines, a charge Phnom Penh denied.

Fighting resumed in December. On 8 December, Thailand launched airstrikes into Cambodia after clashes erupted along their disputed border, with both sides accusing each other of breaching the US-brokered ceasefire in October.

On 12 December, after calls with both leaders, President Trump stated that Thailand and Cambodia had agreed to “cease all shooting” and revert to the prior accord. But, on 13 December, Thailand vowed to continue military actions until threats were neutralised, while Cambodia reported ongoing bombings and maintained that it seeks a peaceful resolution. The renewed fighting in December is the most serious since the five-day exchange in July.

Between 22 and 29 December, renewed diplomatic efforts led to de-escalation. ASEAN foreign ministers met in Kuala Lumpur, defence talks resumed between Thailand and Cambodia, and on 27 December, defence ministers of both countries signed a second ceasefire. This ended nearly three weeks of fighting that killed at least 101 people and displaced over half a million civilians. On 29 December, both sides agreed to gradually consolidate the ceasefire, following trilateral talks hosted by China.

What are the issues?
First, contested sovereignty over un-demarcated border areas. The core issue is the dispute over un-demarcated sections of the 817-km border, inherited from colonial-era treaties concluded in 1904 and 1907 between France (which ruled Cambodia) and Siam (present-day Thailand). According to the agreements, the boundary was set to follow the Dangrek Mountains watershed, but the French-drawn maps placed key ancient Khmer temples, particularly Preah Vihear, on the Cambodian side. The 11th century Hindu temple Preah Vihear, or Khao Phra Viharn in Thailand, has been central to the dispute, with both countries claiming historical ownership. In 1962, the International Court of Justice (ICJ) ruled that Preah Vihear belonged to Cambodia, although the surrounding promontory remained contested. Later, in 2013, the ICJ clarification affirmed Cambodian sovereignty over most of the area. Other disputed sites include Ta Moan and Ta Krabei, both ancient Khmer temples located in the Dangrek Mountains along the un-demarcated border between Thailand’s Surin province and Cambodia’s Oddar Meanchey province.

Second, domestic politics and nationalism aggravate the issue. Nationalist sentiments in both countries add to the issue, with ancient temples of Preah Vihear reflecting historical Khmer glory and cultural pride for Cambodia, while representing territorial integrity and sovereignty for Thailand. Disputes over these sites have repeatedly led to nationalist fervour, as seen in the 2003 riots in Phnom Penh over remarks on Angkor Wat and deadly clashes from 2008-2011 triggered by Cambodia's UNESCO listing of Preah Vihear. In 2025, this pattern resurfaced. Following the clashes in July, Reuters reported that a wave of nationalism boosted public support for Cambodia's government on social media. News reports show that Thailand’s Prime Minister Anutin Charnvirakul tapped surging nationalist sentiment over the clashes to improve his appeal ahead of snap elections.

Third, the fragile mediation efforts. Since the major clashes in 2008-11, there have been several mediation efforts involving ASEAN, the ICJ, and external actors to resolve the dispute, but failed. In 2011, ASEAN, under Indonesia’s chairmanship, played a key role. It proposed deploying Indonesian observers to monitor a ceasefire and support troop withdrawals from a provisional demilitarised zone ordered by the ICJ that year. Meanwhile, Cambodia sought clarification from the ICJ, which in 2013 reaffirmed its sovereignty over much of the Preah Vihear promontory. But Thailand resisted any third-party involvement and preferred bilateral talks, which limited implementation. In 2025, renewed fighting in July led to fresh mediation efforts. Initial outreach came from Malaysia, as ASEAN chair, and China, but these efforts produced limited progress. A temporary breakthrough followed in July, when President Trump held calls with leaders in Bangkok and Phnom Penh; his threats of 36 per cent tariffs on exports to the US, their biggest market, led to an unconditional ceasefire, which was mediated by Malaysia. The ceasefire was expanded into a detailed agreement in October, witnessed by Trump, committing both sides to phased troop and heavy weapons withdrawals, prisoner releases, and de-mining operations. However, Thailand accused Cambodia of violating commitments, including laying new landmines, and suspended participation in November. Cambodia denied the allegations, viewing Thailand’s actions as aggressive.

What does it mean for 2026?
First, a restored ceasefire and risk of recurrence. The second ceasefire signed on 27 December ended the deadliest clashes since 2011, allowing the gradual return of over half a million displaced people and conditional prisoner releases. However, clashes between the two risk recurrence if border ambiguities, competing claims of encroachment, landmine use, and entrenched nationalist narratives remain unaddressed. At the border level, verifiable troop withdrawals, joint de-mining, and direct military communication must be prioritised to prevent an escalation. At the bilateral level, sustained engagement through joint commissions is necessary for border demarcation and confidence-building.

Second, the limits of external mediation and the need to address structural causes. US influence waned after initial tariff threats that secured temporary pauses. ASEAN, with Malaysia as chair, played a role in reaching the second ceasefire, while China’s late-2025 engagement is focused on consolidating the truce; however both lack enforcement power for long-term demarcation or trust-building. At the core, long-term stability in 2026 and beyond will depend less on external pressure or engagement and more on the willingness of Thailand and Cambodia to address the conflict’s structural causes.

About the author 
R. Preetha is a Postgraduate student at Stella Maris College, Bengaluru. 

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