Thailand’s Deterrence Failure Against Cambodia: A Focus on Structural Hindrances

INTRODUCTION

The collapse of the Thailand-Cambodia “peace deal” six weeks after its signing at the 47th ASEAN Summit is hardly surprising. After all, the fast-tracked peace brokered by Malaysia under American and Chinese oversight was devoid of any organic de-escalation.

Thailand-Cambodia disputes, born of ambiguous colonial-era demarcation and requiring sustained mutual accommodation and concession, repel any quick and conclusive resolution. Hampering this is the routine instrumentalisation of historical grievances for domestic political gains, which is played out contingently alongside government changes and interpersonal ties. This encourages flare-ups, and the conundrum emerges as to why the materially richer Thailand cannot deter the weaker Cambodia.

Deterrence as the prevention of adversarial behaviour is equally about the resolve to act as it is about material means. For Thailand, as a far more capable party militarily and economically, its leaders’ weak resolve has clearly emboldened Cambodia. The follow-up question is what accounts for that resolve gap. Interests of domestic elites, central to Thailand-Cambodia relations and notably salient in 2025, are widely seen as the answer. While relevant, the narrow and fluctuating elite-interest reading cannot quite capture the two belligerents’ persistent behavioural paradox in military and diplomatic posturing.

This Perspective thus turns to structural determinants. In challenging the common assumption that Thailand’s deterrence failure is readily corrected if elites simply put their narrowed institutional and personal interests aside, the paper argues that the Thai resolve deficit is more of a condition than a choice, one grounded in three entrenched structures. These include the conflict’s limited war imperative, Thailand’s geographical multi-front vulnerability, and the lack of external support rooted in the flexibly non-aligned foreign engagement of the country.
The paper explores in order: (1) origins and legalities of Thailand-Cambodia border disputes; (2) their recurring flare-ups and alarming developments in 2025; (3) the elite-interest explanations and their limitations; and (4) structural pressures underpinning Thailand’s indecisiveness.

ORIGINS AND LEGALITIES OF BORDER DISPUTES

Colonial-era treaties define Thailand’s present boundaries. Treaties relevant to the Thai-Cambodian border are those by Siam (Thailand’s name before 1939) and France (Cambodia’s former colonial authority) signed in 1904 and 1907. The 1904 convention established that watershed lines would define the Franco-Siamese frontier, and that a mixed commission would handle surveying and mapping tasks. The 1907 treaty, which saw Siam and France exchanging territories, left intact the boundary lines within the Dangrek range as agreed in 1904. The Annex I map, completed in 1908 by French cartographers rather than the mixed Franco-Siamese commission, nonetheless departed from the watershed principle, placing the ancient Hindu-Buddhist Preah Vihear temple that would come to dominate the Thai-Cambodian conflict within French Cambodia, and to Siam’s disadvantage.

It was not until the 1950s that a formal Siamese protest was lodged against the backdrop of French Indochina’s decolonisation. Thailand moved to occupy Preah Vihear soon after Cambodia gained independence in 1953. In 1959, Cambodia brought the case before the International Court of Justice (ICJ) to seek a settlement on the temple’s ownership, to which Thailand consented. The ruling was made, nine-to-three, in June 1962 against Thailand based on its failure to raise timely objections to the flawed Annex I map.

Elite interests are the most visible driver of Thailand’s weak resolve despite its material edge. At one level, incentives exist for ruling elites to prolong interstate tensions for domestic legitimation or distraction.

The 1962 judgment was, and still is, debatable. In the immediate aftermath, sceptical judges argued that the 1904 treaty’s dictates should prevail when the map’s “acceptance” and all other subsequent developments arose under changing global circumstances, thereby lacking binding effect. Consequently, as later observed by Peter Cuasay in 1998, the ICJ’s reasoning that silence equates to consent counterproductively fosters a kind of “fortress mentality,” under which unrelenting vigilance and confrontation are normalised. Even the smallest incident should be protested, or else it could be seen as a tacit acceptance. The unattainability of lasting Thai-Cambodian cooperation on sensitive matters relating to sovereignty has, in other words, long been foreseen.

If the 1962 judgment is believed to be unfair, then the 2013 interpretation judgment stemming from Cambodia’s 2011 request can be argued to be even more so. By granting Cambodia sovereignty over the temple’s promontory in 2013, the ICJ effectively altered its original ruling on the temple structure, which was supposedly final.

Figure 1: Thailand-Cambodia Border Flashpoints

The Preah Vihear temple is among the many disputed sites (Figure 1), egged on by incompatibly different maps. Whereas Cambodia uses the French-drawn 1:200,000 Annex I, Thailand refers to the 1:50,000 military-made topographic maps. Developing a new mutually acceptable map is the most logical course forward, and this is the long-term objective of the Joint Boundary Commission set up in 1997 as the main bilateral mechanism for land border demarcation. Figure 2 outlines other bilateral channels for border management. The legally non-binding memorandum of understanding signed in 2000 (2543 BE) functions as a governing framework. As of 2025, 602 kilometres of the Thailand-Cambodia border have undergone joint survey—with agreements reached on 45 out of 74 existing boundary pillars—while 196 kilometres have never been marked. Notwithstanding incremental progress, the extent of compromise required and the deep-seated tensions keep the joint map production a Herculean task.

Figure 2: Bilateral Mechanisms for Land Border Management

ESCALATORY CYCLES

Of Thailand’s border disputes (Table 1), contestation with Cambodia is the most emotionally charged and recurring, in turn spotlighting Thailand’s deterrence failure. The 21^st century thus far has witnessed two series of armed clashes, in the 2008-2011 period around Preah Vihear, and now in 2025. One could also include the 2003 burning of the Thai embassy in Phnom Penh by Cambodian rioters. Those riots, sparked by unfounded reports of a Thai actress’ remark that Angkor Wat belonged to Thailand, reflect the broader struggle over stone temples tied to centuries of national identities and sub-regional hierarchy.

Siam historically exercised suzerainty over Cambodia, and for Cambodian leaders to regard Thailand essentially as an imperialist that needs to be fended off is only natural. From Thailand’s perspective, Cambodia occupies a similar position to Laos as a “lost territory” or a Siamese subordinate absorbed into French Indochina. Unlike the quieter Laos, however, post-independence Cambodian leaders from Prince Sihanouk to Hun Sen have shown an assertive, theatrical streak. So Cambodia, to Thai leaders, is a sort of perpetual irritant to be managed.

Their differences translate into divergent preferences in resolving border disputes. The larger Thailand insists on their bilateralism staying flexible and free of external intervention. The smaller Cambodia, with its colonial heritage and past ICJ victories, seeks to internationalise the disputes into legal and diplomatic arenas, where third-party intervention from another state or international body like the ICJ and the UN would likely aid its case.

Cambodia becomes more assertive with each flare-up, especially militarily. Compared to the 2008-2011 case, the 2025 confrontation has seen expanded geographical scope (Figure 1), heavier armaments, and greater civilian harm. Analysis of satellite imagery (Figure 3) indicates that Cambodia, against the 2000 MOU’s Article V (Figure 2), made tactical adjustments in sensitive areas well ahead of the first fatal skirmish on 28 May, and speedily mobilised heavy military assets thereafter.

Thailand’s primary deterrent tool in this initial phase was border closure. But this hurt ordinary Cambodians dependent on Thai medical care, schooling, and micro-trade more than Phnom Penh’s leadership, which can diversify trade ties away from Thailand. Moreover, the closure was arguably untimely and flimsily enforced, starting in early June and hardening only towards the month’s end following Hun Sen’s publicisation of a private phone conversation between himself and former Thai premier Paetongtarn Shinawatra, which exposed Thailand’s leadership disunity.

Thailand’s deterrence failure manifested in mid-July. The watershed escalation saw Cambodia fire BM-21 rockets into Thai territory, hitting a hospital, a gas station, and homes, and killing at least 13 civilians. Simultaneously, Cambodia reportedly opened a new battlefront along the border near the Gulf of Thailand (point 8 in Figure 1). This was brief but significant, moving matters, as it were, beyond the traditional hinterland zone where ancient temples lie.

Intent cannot be determined with certainty. Even so, interpretations that Thai civilian casualties were collateral damage or the result of spontaneous firing and command fragmentation are unconvincing because the BM-21 is explicitly an imprecise area saturation weapon that requires battery-level preparation. The Gulf of Thailand episode, meanwhile, is symbolically powerful as a reaffirmation of Cambodia’s overlapping maritime claims, including its partial claim to Koh Kood. To Thai nationalists, Koh Kood is possibly the most provocative Cambodian claim because the island has long been certified as Thai in both de facto and de jure senses.

Endangering civilians does not seem to help Cambodia’s effort to internationalise disputes in its favour. The operation that risks a maritime spillover, too, is perplexing. First, a numerically inferior state (Figure 4) would rationally avoid a two-front battle. Second, Cambodia at the time possessed virtually no substantive naval capability or experience. Yet these actions are comprehensible within a cost-benefit calculus of Cambodia, inviting forceful enough Thai responses through calibrated provocations, allowing Cambodia to call for talks and present itself as diplomacy-seeking.

Factoring into that calculus must be the confidence that Thailand’s retaliation would be within acceptable bounds and that any potential international intervention on the ground would not work significantly against Cambodian interests. Thailand’s retaliatory deployments of fighter jets against Cambodian military positions along the border likely fell comfortably within what Cambodia anticipated. Plausible deniability, evident in alternative interpretations of Thai civilian deaths by BM-21s, mitigates international scrutiny.

The renewed fighting in December has seen continued Cambodian use of BM-21s and movements near the maritime frontier. Simultaneously, Cambodia declares that it is “ready for talks” anytime. Thai military operations in this phase have become more forceful to neutralise Cambodian capabilities, but without any element of surprise as of writing. These patterns reinforce the calibrated provocations argument.

Figure 3: Chronology of Escalation in the 2025 Border Conflict

Figure 4: Thailand vs. Cambodia Military Comparison

Cambodia’s military boldness works in tandem with concentrated internationalisation efforts. On the core judicial front, Cambodia has sought ICJ arbitration over four contested sites (Figure 1). To rally international sympathy, Cambodia has invoked pointed analogies likening Thailand to “sovereignty violator” Russia and their border dispute to Gaza’s, and accused Thailand’s military of deploying chemical weapons, though this remains unsubstantiated. Withstanding international pressure is difficult when Thailand lacks the kind of global leverage needed to act on its own terms. Ultimately, Cambodia stands to gain whether Thailand is steered towards the ICJ or into a frozen conflict.

ELITES AS THE PROBLEM

Elite interests are the most visible driver of Thailand’s weak resolve despite its material edge. At one level, incentives exist for ruling elites to prolong interstate tensions for domestic legitimation or distraction. If Cambodia’s hereditary autocracy—built overtly on suppression—mobilises the conflict as a space to perform its role as the nation’s indispensable defender of peace, then Thailand, as a polarised partial democracy grappling with civil-military imbalance and growing reform calls, can similarly utilise the conflict to generate rally-around-the-flag effects. Opposition to military dominance is weakened in the process. Tellingly, the People’s Party has become less critical of arms procurement in 2025. Insofar as security anxieties persist, the pro-military path dependence will continue. Political parties vying to take office in the scheduled 2026 election will be inclined to support, not challenge, military priorities.

Another level involves the entanglement of national security and the interests of transnational elite networks. Early in the 2025 flare-up, attention fixated on the rupture between two political-business titans long controversially associated: Thailand’s Thaksin Shinawatra and Cambodia’s Hun Sen. This culminated in the leaked audio that unseated Thaksin’s daughter Paetongtarn and ended the Thaksinite Pheu Thai Party’s two-year control of Thailand’s national government. The abrupt fallout supports the theory that tensions were initially choreographed to deflect the two countries’ worsening economic troubles, and were not supposed to spiral. The subsequent spiralling is commonly attributed to irreconcilable interests in the gambling industry, where Thaksin’s efforts to legalise casinos in Thailand threatened Cambodia’s revenue, and in the gas-rich Gulf of Thailand, where lucrative incentives from energy firms apparently lie.

Thailand’s current government under the Bhumjaithai Party has adopted a military-led posture to avoid being seen as yielding to Cambodia, like its ally-turned-enemy Pheu Thai. The murmurs that elite interests fuel Thailand’s resolve gap nevertheless remain, with the narrative shifting to the government’s initial unhurried tackling of Cambodia’s well-documented scam networks despite a clear opening created for it by US and South Korean anti-scam operations. The slow pace of action is obvious: some Thai politicians and officials have benefited, directly or indirectly, from the illicit revenues involved.

These elite-interest explanations, though sound and useful, are analytically limited. First, they struggle to unpack the inertia across Thai governments. The 2008-2011 border crisis unfolded under a similar pattern of Thai indecisiveness when transnational scam issues were not yet prevalent. Second, due to their opaque and personal nature, elite interests often stay confined to the realm of speculation and risk reducing genuine strategic contestation into a mere consequence of domestic power play. Third, the resolve gap sustained by elite interests is too fluctuating and can be strengthened with dangerous suddenness, as apparent in Thailand’s hardening stance in the December 2025 confrontation. Cambodia’s strategic confidence as a rational actor must thus rest crucially on underlying conditions that would constrain even the most cohesive and determined Thai leadership.

STRUCTURAL SHACKLES

Limited War Rationale

The paradox of a limited war applies to Thailand as it confronts Cambodia. For materially richer powers, limited wars involving restrained use of force to manage threats at hand are harder to win—in a sense of achieving durable “peace” on one’s own terms—than total wars involving all-encompassing mobilisation of national resources for unconditional victories. Since limited wars rarely dislodge the adversary’s leadership structure, flare-ups recur. Knowing that the stronger powers’ natural advantages are blunted, weaker powers can engage in provocations without fearing existential retaliation. Limited wars are also a norm, by default and not choice, in the interdependent and norm-bound international system after World War II.

To improve its crisis management and to make its signalling more credible, Thailand requires institutional change to establish a highly centralised command encompassing both military and civilian agencies, akin to what it has in the maritime sphere—the Thai Maritime Enforcement Command Centre—which has proven effective in times of “conflicts.” 

The classical Clausewitzian understanding of war is that it is a continuation of politics by other means. This conception inherently involves struggles over legitimacy and perception, meaning that even a measured Thai response risks being narratively weaponised by Cambodia. A case in point is Thailand’s F-16 and Gripen deployments against Cambodian military targets in July 2025. As a response to Cambodian rockets fired into Thai territory that killed around a dozen civilians, whether intentional or accidental, Thailand’s limited airstrikes were a proportionate exercise of its right to self-defence. But perceptions are shaped more easily by visibility than strict proportionality. The spectacle of attacking fighters projects an image of greater aggression and asymmetry, and its continued use would complicate future Thai arms acquisitions. At the height of July’s fighting, Thailand was finalising a deal to purchase more Swedish Gripens against Cambodia’s lobbying. Although Cambodia failed to change Sweden’s mind this time, the same favourable outcome is not guaranteed in the future and in Thailand’s dealings with other countries.

The Burden of Geography

States with fewer land borders are structurally safer than those bordered by multiple continental neighbours. Thailand shares long land borders with four neighbours, a significant portion of which remains un-demarcated and security-sensitive, exposing the country to multidirectional security pressures.

Table 1 shows that the Thailand-Myanmar frontier is the most vulnerable and will only grow in strategic importance amid the intensifying geopolitical competition over critical minerals. This priority makes it easy for Thailand to sideline Cambodia. Just months before Cambodia’s first satellite-detected activity (Figure 3), Thailand faced an alarming incursion from the United Wa State Army, one of Myanmar’s most formidable ethnic armed groups.

Needless to say, simultaneous heightening in tensions elsewhere could stretch Thailand’s current management of the Thai-Cambodian front unacceptably thin. By contrast, the geographically much smaller Cambodia identifies Thailand as a primary threat. It therefore tends to move more proactively to offset any perceived dangerous Thai movement.

Table 1: Overview of Thailand’s Land Border

Thailand-Bordering State	Approximate Length (km)	Implications
Thailand-Cambodia	798 (over half demarcated)	– Prone to episodic state-to-state clashes, especially in the northern section that houses key contested sites. – The southern section has maritime-strategic significance, being close to the disputed maritime area in the Gulf of Thailand and the much-watched Cambodian Ream Naval Base. It is also close to Thailand’s Eastern Economic Corridor. – Scam activities targeting Thais are concentrated in Poipet and Sihanoukville.
Thailand-Laos	1,810 (over 90 per cent demarcated)	– Relatively peaceful. Security concerns focused on transnational crime around the Golden Triangle. – Importance lies in strategic connectivity (China-Laos-Thailand railway).
Thailand-Myanmar	2,401 (only 59 km conclusively demarcated as of 2024)	– Most complex and chronically volatile, given the long frontier and Myanmar’s nature as a civil war-torn and resource-rich country. Daily cross-border crimes, refugee inflows, and armed encroachments (by the Myanmar military and ethnic armed organisations alike) are key features. – Notorious scam activities around the Myawaddy-Mae Sot crossing. – Strategic importance tied to critical minerals and energy pipelines.
Thailand-Malaysia	647 (over 90 per cent demarcated)	– Most sensitive internally. Thailand’s three Malay-Muslim-majority southernmost provinces have long been engulfed in low-intensity and contained separatist insurgency. The insurgency is ethno-nationalist, with localised jihadist rhetoric. – The region’s main rebel group, Barisan Revolusi Nasional (BRN), is becoming more capable. – Malaysia acts as a mediator but is not recognised as an honest broker, as parts of its government sympathise with the BRN.

Lack of International Backing

A New York Times article published in late September cited Thai intelligence documents revealing that just weeks before July’s confrontation, Chinese rockets, artillery shells, and mortars were shipped to Cambodia, packed into 42 containers, and transported to the border. The Chinese Embassy in Bangkok denied the allegation, saying that China, as a friendly neighbour to both belligerents, has not armed Cambodia against Thailand and that Chinese weapons operated by Cambodia came from existing military cooperation. Shortly afterwards, however, the Chinese ambassador to Phnom Penh issued a contradictory statement that read, “China firmly supports Cambodia in safeguarding its national sovereignty, security and development interests, and will always be a reliable partner in Cambodia’s development.”
It is certainly fair to say that Chinese weapons shipments were ill-timed rather than intentional, given the deepening of Thailand-China ties, including in defence. Still, the longstanding client-state-like closeness of Cambodia-China relations makes some degree of Chinese favouring of Cambodia structurally expected.

Meanwhile, the US, as Thailand’s treaty ally, has approached Cambodia with an unusual friendliness, lifting a four-year arms embargo and greenlighting the resumption of the US-Cambodian “Angkor Sentinel” military drill suspended since 2017. This is most straightforwardly interpreted within the US-versus-China context, with Washington seeking to expand its influence over the increasingly receptive Cambodia.

More broadly, Thailand has been unable to convince the international community to exert serious diplomatic pressure on Cambodia over its Soviet-originated PMN-2 landmines that have repeatedly injured Thai troops. This is despite expert assessments supporting Thailand’s claim that the PMN-2s were newly laid. And even if they are relics of past wars, as Cambodia insists, that significant areas along its contiguous territory with Thailand remain contaminated today is questionable. The Mine Ban (Ottawa) Convention, which entered into force in 2000 for Cambodia, dictates complete clearance within ten years. Two extensions of that ten-year clearance window have already been granted to Cambodia. With a third extension due for review in December 2025, Thailand’s Foreign Minister Sihasak Phuangketkeow has finally called for a “fact-finding mission.” Prospects are nevertheless limited when neither the US nor China is party to the Ottawa Convention, while even current signatories are withdrawing under security pressures—some in Europe confronting Russia, for that matter.

Coming under scrutiny with these developments is the sustainability of Thailand’s flexible foreign policy. Since the colonial encroachment, Thailand has accommodated powerful states’ interests while resisting their overreach to safeguard its autonomy. The approach served Thailand well in earlier eras, but only because threat landscapes then were more ordered, and because Thailand, in survival mode, had clearer alignments and a readiness to reverse them when necessary. In today’s fragmented geopolitical environment, where Thailand faces ambient danger but nothing existential in the traditional sense, Thai foreign policy has turned largely into a passive projection of neutrality. Unfortunately, this leaves Thailand in the position of suffering the adage “a friend to all is a friend to none” when challenges arise, and robust external backing becomes valuable.

These structures illuminate why China has made no real attempt to stop Cambodia from wielding Chinese weapons against Thailand and why the US, especially under the Trump administration, with little appetite for alliance maintenance, has not stood by Thailand. Both superpowers know full well that Thailand, being a devoted hedger, would not tilt meaningfully against them.

CONCLUSION

As a materially modest power vis-à-vis Thailand, Cambodia’s boldness reflects not strength on its part per se, but weakness on the Thai side. Thailand’s resolve deficit that accounts for its deterrence failure is shaped principally by rigidly embedded structures, namely the limited war rationale, border geography, and the foreign policy path dependence. Recognising this interplay is important for understanding that even without narrow elite interests, Thailand’s deterrence will not improve dramatically.
This analysis seeks to set the stage for policymakers to see that Thailand can still make realistic, modest steps through intelligent manoeuvring of structural constraints to better position itself in a conflict that is essentially a time-bomb. For starters, Thailand would need to move beyond being overly apprehensive about the conflict’s internationalisation. That has already happened and will surely deepen. Accordingly, Thailand must articulate a clearer narrative justifying its refusal to engage the ICJ.
Next comes greater cooperation with regional partners who share the same concerns about external intervention. Vietnam, being similarly included in Cambodia’s narrative of a smaller nation’s security at the hands of larger neighbours and sharing Thailand’s geography-driven multi-front insecurity, is a natural partner, as is Indonesia, ASEAN’s natural leader due to its size and the strongest ideological non-alignment.
To improve its crisis management and to make its signalling more credible, Thailand requires institutional change to establish a highly centralised command encompassing both military and civilian agencies, akin to what it has in the maritime sphere—the Thai Maritime Enforcement Command Centre—which has proven effective in times of “conflicts.” On credible signalling, whereas some states may over-communicate and lose the value of ambiguity, Thailand’s problem is the lack of a clearly defined red line. That must be addressed as one of the top priorities.

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This is an adapted version of ISEAS Perspective 2025/107 published on 19 December 2025. The paper and its references can be accessed at this link.