Why have Thailand-Cambodia border clashes flared up again? | Explained Today World News

The story so far: On December 8, Thailand launched airstrikes into Cambodia after clashes erupted along their disputed border, with both sides accusing each other of breaching the U.S.-brokered ceasefire in October. On December 12, after calls with both leaders, President Trump stated that Thailand and Cambodia had agreed to “cease all shooting”. However, Thailand has vowed to continue military actions until threats are neutralised.

What happened early this year?

In May 2025, tensions between the two countries escalated when a Cambodian soldier was killed in a skirmish, leading to troop buildup and diplomatic strains. July witnessed five days of intense fighting involving artillery, rockets, and Thai airstrikes that killed at least 48 people and displaced over 3,00,000. A ceasefire was brokered through U.S. pressure and Malaysian mediation, ending the tensions. The truce was formalised in October with an agreement signed in Kuala Lumpur. However, in November, Thailand suspended its implementation after a landmine injured a soldier. It accused Cambodia of planting new mines.

On December 7 and 8, clashes renewed, escalating to Thai airstrikes targeting Cambodian military sites, including alleged rocket positions. As of now, casualties include over 15 Thai soldiers and dozens on the Cambodian side, along with mass civilian evacuations.

What is the border dispute about?

The core issue is sovereignty 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) respectively. These agreements planned for the boundary 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 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.

Nationalist sentiments in both countries complicate the bilateral issue, with temples reflecting historical Khmer glory for Cambodia and territorial integrity for Thailand. Between 2008-2011, deadly clashes occurred after Cambodia tried to list Preah Vihear as a UNESCO World Heritage site.

How have mediation efforts fared?

Since the major clashes in 2008-11, several mediation efforts involving the Association of Southeast Asian Nations (ASEAN), the ICJ, and external actors, aimed at resolving the dispute, have 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 demilitarised zone ordered by the ICJ that year. But Thailand resisted any third-party involvement.

In 2025, renewed fighting in July led to fresh mediation efforts. President Trump held calls with leaders in Bangkok and Phnom Penh; his threats of 36% tariffs on exports to the U.S., their biggest market, led to an unconditional ceasefire.

What is the way forward?

At the border level, de-escalation should build on measures attempted under the October agreement, including verifiable troop withdrawals, joint de-mining, and direct military communication. At the bilateral level, sustained engagement through joint commissions is necessary for border demarcation; Thailand’s preference for bilateral talks must be reconciled with Cambodia’s openness to third-party involvement.

R. Preetha is pursuing a postgraduate degree at Stella Maris College, Chennai and is currently a Research Assistant at NIAS, Bengaluru.