The Expanding Border War Between Thailand and Cambodia

Southeast Asia is currently in crisis as the neighbor nations of Thailand and Cambodia trade heavy fire across their border zone. This marks the second time the two countries have engaged in open hostilities this year. A fragile ceasefire, originally implemented with the assistance of Washington, D.C., has completely fallen apart.

Both sides are speaking and acting as if they expect these battles to intensify significantly before any resolution is reached. Hundreds of thousands of civilians have fled the conflict zone, with both nations claiming the other is to blame for the violence. Thailand, possessing by far the stronger military of the two nations, has made it clear that it will not accept anything short of a total victory.

When Thailand and Cambodia fought their first recent exchange in July, the situation was already dire. In this latest escalation, both sides know precisely what they are getting into, fully understanding the balance of power, and neither will have an easy time backing down. As munitions fall across the region, a critical question remains: Can this be contained as a minor territorial dispute, or is this the onset of a new, all-out war?

Historical Context and the Rise of Nationalism

To understand the course of this expanding conflict, it is necessary to examine the historical context driving these two nations. Thailand and Cambodia share a very long and troubled history, marked by a poorly defined, disputed border zone that has been a point of contention for more than a century. This border zone is highly important to both nations, largely due to the dense concentration of cultural and historical sites in the area.

Conflict over this territory is not a new phenomenon; between 2008 and 2011, Thailand and Cambodia engaged frequently in minor skirmishes. During that period, however, both sides tended to demonstrate a mutual desire to avoid fighting a larger-scale war. Both nations have undergone a significant transformation in recent years.

This shift is not the result of a changing strategic situation, but rather the rapid rise of nationalism on both sides of the border. When discussing nationalism in the context of this conflict, the focus rests less on a specific ideology and more on the sheer power of the movement itself. From a political standpoint, nationalism serves as a highly potent driver of political momentum.

Leaders in Thailand and Cambodia who can build and capitalize on these nationalist movements generally see their political fortunes improve dramatically. Consequently, Thai and Cambodian nationalist movements have swelled in size and power over the last couple of decades, largely defining themselves in direct opposition to one another. Cultural issues, international disputes, rhetorical differences, and that highly disputed, culturally significant border zone have provided fruitful targets for political leaders in both Bangkok and Phnom Penh.

As nationalist movements have taken on a life of their own, it has become increasingly difficult for leaders to justify backing down from what might otherwise be an avoidable fight. In the first half of 2025, when tensions in the border zone started to escalate once again, political leaders in both countries attempted to capitalize on the fervor. In late May, a skirmish between Thai and Cambodian soldiers left one Cambodian dead, an event that hardliners in both nations took as a grave affront.

Tensions continued to rise as both sides blamed each other for the aggression. By mid-June, Thailand’s then-prime minister was caught on leaked audio speaking deferentially to Cambodia’s Senate president and de-facto leader, Hun Sen. This revelation incensed many in Thailand while emboldening factions in Cambodia, leading pragmatic observers in both nations to realize the situation was rapidly getting out of hand.

The July Clashes and the Breakdown of the Ceasefire

A military confrontation between Thailand and Cambodia is far from an equal fight. Thailand is a United States ally with a relatively strong and modern military across its air, land, and sea domains. In contrast, Cambodia’s military is not only woefully unequipped, but has also been characterized as corrupt and unprofessional.

In a scenario where cooler heads prevailed, the escalating tensions would have presented an ideal moment to de-escalate. Instead, what followed were border closings, political upheaval, diplomatic breakdown, and eventually several days of open hostilities in late July. The human cost of this initial exchange was severe.

Roughly 150,000 Thais and 135,000 Cambodians were displaced due to the fighting. About two dozen civilians were reported killed, and while the two nations officially acknowledged a combined thirty-seven dead soldiers, the true death toll is likely to have been much higher. Under heavy pressure from Washington and a range of regional actors, the two sides eventually agreed to a ceasefire, which the international community initially hoped would bring an end to the conflict.

However, the larger catastrophe was only just beginning. Regardless of the narratives pushed by both governments, the outcome of the first exchange was fairly clear. While Cambodia could certainly inflict damage, Thailand held a distinct upper hand, to the extent that Cambodia would have been foolish to avoid securing a ceasefire.

Shortly after the fighting stopped, it became evident that the intense nationalism driving the initial border clashes would continue pushing both governments toward future confrontation. Neither government exerted significant effort to defuse the situation; Thai leaders pointed to their clear superiority in battle, while Cambodian leaders highlighted their willingness to stand their ground, allowing both to push a narrative of domestic victory. Over the following months, the fragile peace eroded completely.

Thailand repeatedly accused Cambodia of planting new landmines in the border region, a direct violation of the anti-landmine Ottawa Treaty to which both nations are signatories. Cambodia, in turn, accused Thailand of planning new strikes and offensives. Thailand claimed Cambodia was failing to recover the bodies of deceased soldiers, posing a health hazard, while Cambodia accused Thailand of erecting new barriers in sovereign Cambodian territory.

Tensions flared further as Thailand kept eighteen Cambodian prisoners of war in custody, and multiple Thai soldiers were injured by landmines. By late October, the two nations signed a comprehensive, U.S.-brokered ceasefire deal in Kuala Lumpur. Yet, barely two weeks later, after another landmine claimed the right foot of a Thai soldier, Thailand announced the indefinite suspension of the ceasefire.

Resumption of Hostilities and the Thai Ultimatum

Throughout a very tense November, both militaries began moving assets toward the border zone. In early December, Thailand raised alarms that Cambodian assets were poised to strike civilian areas, and shortly thereafter, the fighting resumed. Similar to the first round of violence, these clashes took place primarily in remote or isolated areas where reliable civilian reporting remains scarce.

In these zones, both Thailand and Cambodia possess strong incentives to inflate their victories, downplay their losses, and accuse the other side of instigating the combat. Regardless of which forces initiated the exchange, the clashes restarted on December 7 and escalated substantially the following day. On December 8, Thailand took credit for a series of airstrikes across the border region while accusing Cambodia of launching rockets into civilian-settled areas.

During this intense escalation, Thai F-16 fighter jets laid waste to Cambodian artillery positions. Ground battles broke out across multiple provinces, forcing civilians to evacuate urgently from the combat zone for the second time in the same year. As the day progressed, Thailand issued a strict ultimatum to Cambodia: accept a ceasefire by mid-evening, or Thailand would remove all limitations on its use of force and leverage its full military strength against Cambodian positions.

It remains unclear whether Cambodia refused to accept those terms due to military realities on the ground or the domestic political backlash that would have followed a perceived surrender. Ultimately, the underlying reasoning mattered little to the outcome on the battlefield. Cambodia did not accept Thailand’s ultimatum.

Starting on Tuesday, December 9, the conflict expanded significantly, pushing the region further away from any immediate diplomatic off-ramp.

Strategic Implications and the Asymmetric Threat

By the early-morning hours of Wednesday, December 10, the fighting between Thailand and Cambodia appeared to be steadily rising in intensity. Thailand reported that its tanks had fired upon a border casino complex that the Cambodian military had commandeered as a storage depot. Meanwhile, Thai F-16s and other fighters carried out a series of strikes against claimed strategic targets.

Cambodia stated that its troops spent the day attempting to defend the country against unprovoked Thai aggression. Furthermore, Thailand accused Cambodia of unleashing massive barrages of rockets and artillery, alongside utilizing small drones to drop explosives—tactics mirroring those seen in the war in Ukraine. The Thai Navy also indicated operations in coastal regions, while Cambodian civilians reported constant cross-border shelling.

The international community, led by the United States, has attempted to push for an immediate peace. The incumbent Trump administration has maintained a strong interest in preserving the earlier ceasefire, which it had touted for months as a major diplomatic triumph. However, the political environment in Thailand has shifted, making peace much harder to achieve.

Thai leaders have signaled to the global press that their objective is no longer simply to secure the disputed border zone, but rather to entirely destroy Cambodia’s ability to pose a future threat. One high-level Thai general declared that the military will now work to cripple Cambodia’s military capability for a long time to come. Thailand’s Prime Minister further cemented this stance, stating that the government has already given its commitment to the armed forces to fully carry out the planned operations.

This drastic shift in strategic thinking indicates a deeply troubling trajectory for the conflict. While Thailand commands far greater military force and holds a massive advantage in conventional engagements, dismantling an adversary’s long-term fighting capacity is a notoriously difficult objective. Similar to how Israel has discussed its offensives against Hamas and Hezbollah, a favorable military disparity does not guarantee an easy victory.

Although Thai aircraft, tanks, and artillery are superior and can destroy Cambodian equipment in head-to-head fights, Cambodia retains the capability to fight asymmetrically using ground troops, landmines, drones, and small, mobile assets. If Thailand continues its current campaign, it may only be a matter of time before Cambodia is forced to permanently adopt this guerrilla approach. The transition to asymmetric, guerrilla warfighting is not easily reversed, and the dense, difficult terrain of the border region offers Cambodia a highly effective environment for such tactics.

Diplomatic observers hold out hope that Thailand will be content to destroy key Cambodian military hardware, prove its strategic dominance, and then abide by a new ceasefire. At the same time, the international community must apply pressure on both nations—holding Cambodia to its word when it signals a desire for peace, and restraining Thailand’s overwhelming military advantage. The window to resolve this crisis and prevent a protracted, devastating war in Southeast Asia is closing rapidly.

Sources

1. https://www.reuters.com/world/asia-pacific/thailand-cambodia-fighting-spreads-along-contested-border-2025-12-09/
2. https://www.reuters.com/world/asia-pacific/thailand-says-tariffs-must-not-be-used-force-peace-with-cambodia-2025-12-09/
3. https://apnews.com/article/thailand-cambodia-combat-border-dispute-142145d84a217ad6c6f208769c447615
4. https://www.washingtonpost.com/world/2025/12/09/thailand-cambodia-combat-border-dispute/ac91fd9c-d4bf-11f0-a93c-a869cf73ebd6_story.html
5. https://abcnews.go.com/International/7-civilians-killed-thousands-displaced-amid-thailand-cambodia/story?id=128233661
6. https://www.reuters.com/business/aerospace-defense/china-made-rocket-among-triggers-thai-airstrikes-into-cambodia-2025-12-08/
7. https://www.nytimes.com/2025/12/09/world/asia/thailand-cambodia-border-conflict-evacuation.html
8. https://www.aljazeera.com/news/liveblog/2025/12/9/thailand-cambodia-live
9. https://www.bbc.com/news/live/c4g5e1p585qt
10. https://www.reuters.com/world/asia-pacific/thai-army-says-air-strikes-launched-along-disputed-border-area-with-cambodia-2025-12-08/
11. https://www.telegraph.co.uk/world-news/2025/12/09/why-are-thailand-and-cambodia-fighting-again/
12. https://www.theguardian.com/world/2025/dec/09/fatal-thailand-cambodia-clashes-spread-along-contested-border-area
13. https://www.nytimes.com/2025/12/08/world/asia/thailand-cambodia-border-fighting-strikes.html
14. https://www.france24.com/en/asia-pacific/20251209-cambodia-retaliates-clashes-thailand
15. https://www.cfr.org/blog/real-reasons-thai-cambodia-conflict