Five days that shook ASEAN: How the Cambodia-Thailand border clash became a superpower showdown

WRITTEN BY CHHAY LIM AND CHANDARITH NEAK

3 October 2025

On 24 July 2025, a long-simmering border dispute between Cambodia and Thailand erupted into the most intense fighting the two neighbours had seen in over a decade. The dispute itself was not new — contested markers and overlapping claims around temple sites have sparked intermittent confrontations for decades. What was different this time was both the speed and the response. Over just five days, exchanges of artillery fire, airstrikes, and heavy weapons killed at least 38 people and displaced over 300,000 residents along the border. Then, almost as suddenly as it began, the fighting stopped on 28 July 2025, with a ceasefire mediated by Malaysian Prime Minister Anwar Ibrahim.

This abrupt halt was not merely a function of ASEAN diplomacy. While Malaysia convened the ceasefire talks under its ASEAN Chairmanship, the momentum came from outside the region. Within days, both Washington and Beijing had entered the picture — each applying pressure, each seeking credit. A local conflict quickly became another arena of great-power rivalry, ominously echoing the Cold War period when Southeast Asia was carved into competing spheres of influence. Unless ASEAN strengthens its institutional capacity to resolve disputes among its members before they draw in external intervention, the region risks sliding back into forced alignments and divisions.

The ghost of Cold War divisions: US and China’s responses

The July crisis should be understood against the backdrop of Southeast Asia's traumatic experience with forced alignment during the Cold War. In the 1960s, as American Professor Ann Marie Murphy's analysis shows, anti-communist ASEAN states formed a geostrategic arc of US allies around the South China Sea, enclosing Vietnam and its Chinese backer. Countries like Thailand, the Philippines, Malaysia, and Singapore deliberately aligned with the United States, while Cambodia, Laos, and Vietnam found themselves in China's orbit.

Without institutional mechanisms that both parties accept as legitimate and binding, border disputes remain vulnerable to escalation and external intervention whenever domestic political pressures or regional tensions rise.

This division had devastating consequences. The US military involvement in Vietnam eventually spread to Cambodia and Laos, leaving behind a legacy of unexploded ordnance, social trauma, and economic devastation. When American priorities shifted in the 1970s, Cambodia experienced what many consider one of history's greatest betrayals — abandonment to the Khmer Rouge while Washington pursued rapprochement with Beijing. The lesson for contemporary Cambodian leaders is stark: great power patronage can evaporate as quickly as it materialises.

Donald Trump's intervention in the July crisis exemplified what Murphy identifies as a fundamental shift in US grand strategy — from values-based engagement to purely transactional, power-based tools. Trump did not invoke the US-Thai defence treaty or speak of regional stability. Instead, he reached for his signature instrument: economic coercion. He threatened both Phnom Penh and Bangkok with a 36 per cent tariff on exports unless they accepted a ceasefire, warning that trade talks would be frozen indefinitely.

This approach mirrors the Cold War pattern of using economic leverage to force alignment, but without the ideological framework or long-term commitments that once accompanied such pressure. The intervention was quintessentially Trumpian: transactional, immediate, and effective in pushing Thailand — initially reluctant to accept mediation — to agree to Malaysian-hosted talks.

The dismantling of USAID — which provided USD 3 billion in development assistance to Cambodia over decades — signals a complete departure from the Cold War model of supporting allied governments through thick and thin. Instead, Southeast Asian nations now face what Murphy describes as dealing with a ‘landlord seeking rent’ — extracting immediate compliance without offering long-term security guarantees.

On the other hand, China's measured response to the July crisis reflected lessons learned from its own Cold War experience. Beijing initially emphasised ASEAN's role in mediation, with Chinese ambassador Ouyang Yujing serving as a co-facilitator alongside US ambassador Edgard Kagan in the Malaysian-mediated talks. Unlike the 1960s when Chinese leaders preferred to whittle away at US power via proxies, today's China operates with greater confidence but similar caution.

China's eventual pledge of humanitarian assistance and reconstruction support to affected areas — filling gaps left by American withdrawal — represents a more sophisticated version of Cold War competition. Rather than supporting proxy conflicts, Beijing now offers development assistance and economic integration as tools of influence, demonstrated by the informal meeting China hosted in Shanghai to reinforce ceasefire commitments. 

Cambodia's response to the July crisis reflects hard-learned lessons from its Cold War trauma: hedging, not rigid alignment, offers the best insurance against future betrayal. The country's decision to publicly thank Donald Trump — even nominating him for the Nobel Peace Prize on 7 August 2025 — while deepening coordination with China, demonstrates sophisticated hedging rather than the binary choices that characterised the 1960s.

ASEAN's critical moment: Malaysia's leadership and the Philippines' inheritance

The five-day war revealed both ASEAN's potential and its vulnerabilities. Malaysian Prime Minister Anwar Ibrahim's successful mediation demonstrated what effective ASEAN leadership can achieve, but the need for US and Chinese co-facilitation underscored the organisation's dependence on great power endorsement. The establishment of the General Border Committee meeting in Kuala Lumpur on 7 August 2025, where both sides thanked Malaysia for its crucial role in brokering peace, shows that ASEAN centrality can work — but only when backed by decisive action.

Malaysia's 2025 chairmanship must build a legacy of strong ASEAN centrality by ensuring that member states resolve their historical conflicts quickly through multilateral mechanisms. Under the theme "Inclusivity and Sustainability", Malaysia has positioned itself to set new standards for global governance, revolving around long-lasting values of inclusivity, diversity, and future-oriented planning. The Cambodia-Thailand dispute, rooted in ambiguities from the Franco-Siamese Treaties of 1904 and 1907, exemplifies how unresolved colonial-era boundaries become vulnerabilities that great powers can exploit. Thailand's refusal to accept International Court of Justice jurisdiction since the 1960s, while insisting on bilateral mechanisms, perpetuates the kind of institutional weakness that invites external intervention.

Malaysia's leadership approach, guided by Anwar Ibrahim's Madani philosophy emphasising good governance and people-led growth, presents a critical opportunity to strengthen regional cohesion. As a founding member of ASEAN, Malaysia's chairmanship arrived at a pivotal moment, when the bloc faces unprecedented challenges from heightened geopolitical tension and persistent divisions. How Malaysia manages this role will set crucial momentum for successive chairs — the Philippines in 2026 and Singapore in 2027 — both also founding members who must continue building on this foundation.

The Philippines chairmanship in 2026 must carry forward the institutional strengthening that Malaysia has initiated, further consolidating ASEAN's capacity for "cleaning our own house". ASEAN cannot afford to leave disagreements and unresolved conflicts to drag on, as these create openings for outside powers to pursue their geopolitical interests at the region's expense. The Philippines, with its own experience of great power pressures and scheduled to assume the rotating Chair as ASEAN faces continued external challenges, understands the stakes involved in building the stable and prosperous community that the organisation envisions. 

The imperative of multilateral resolution: ASEAN's choice between centrality and marginality

Both Thailand and Cambodia must recognise that their historical conflicts require swift resolution through established multilateral frameworks — whether the ICJ, ASEAN mechanisms, or other international arbitration — or risk inviting interventions by great power competition with consequential tragedy. The crisis showed how quickly local disputes become stages for external rivalry when institutional mechanisms remain weak or unused.

Thailand's continued resistance to ICJ jurisdiction since 1960 — shared by 118 other UN member states — and preference for bilateral resolution mechanisms perpetuates the very conditions that made great power intervention both possible and necessary in July. This stance persists despite the ICJ's clear 2013 ruling that unanimously affirmed Cambodia's sovereignty over "the whole territory of the promontory of Preah Vihear" and Thailand's obligation to withdraw military forces from the area. Even as recently as June 2025, tensions continued with Cambodia's submission to the ICJ regarding additional temple sites including the Emerald Triangle, Ta Moan Thom, Ta Moan Tauch, and Ta Krabei temples.

The fundamental challenge is that lasting peace requires both sides to engage in comprehensive dialogue and demarcate their borders definitively. However, this process may ultimately require binding third-party arbitration, given the deep history of mistrust and Thailand's rejection of multilateral judicial mechanisms. The ICJ's lack of formal enforcement powers — leaving implementation to the politically-driven UN Security Council where permanent members can exercise veto power — further complicates resolution. Without institutional mechanisms that both parties accept as legitimate and binding, border disputes remain vulnerable to escalation and external intervention whenever domestic political pressures or regional tensions rise.

The political fallout that led to former Thai Prime Minister Paetongtarn Shinawatra's removal from office demonstrates how unresolved border disputes can destabilise domestic politics, creating additional vulnerabilities that external powers can exploit. ASEAN must take ownership of these conflicts before they spiral beyond regional control.

Malaysia's successful mediation, culminating in the 13-point agreement and joint commitment to peaceful resolution, demonstrates that ASEAN centrality can work when backed by decisive leadership. But this success came perilously close to failure — Thailand initially resisted mediation, and only Trump's tariff threats provided sufficient pressure to bring all parties to the table.

The task ahead is urgent: ASEAN must strengthen its institutional capacity to resolve member disputes before they require great power intervention. Malaysia's chairmanship has shown the way, but the Philippines and subsequent chairs must build on this foundation. The alternative — allowing historical grievances to fester until they explode into crises requiring external resolution leads only to the kind of tragedy that Cambodia experienced when the Cold War powers abandoned it to pursue their own rapprochement.

For Cambodia specifically, the July crisis demonstrated that hedging offers better protection than exclusive alignment with either power. But even sophisticated hedging cannot substitute for strong regional institutions that prevent local conflicts from becoming great power competitions in the first place.

Southeast Asia must choose: either ASEAN takes responsibility for cleaning its own house and building the stable, prosperous community it envisions, or the region risks becoming once again a chessboard for external powers playing games with our own people's lives. The July ceasefire was a vital first step — but only if it leads to the institutional strengthening that prevents such crises from recurring.

DISCLAIMER: All views expressed are those of the writer and do not necessarily represent that of the 9DASHLINE.com platform.

Authors biography

Chhay Lim is Designated Deputy Director of Center for Southeast Asian Studies (CSEAS), Institute for International Studies and Public Policy, Royal University of Phnom Penh.

Chandarith Neak is Director of Institute for International Studies and Public Policy, Royal University of Phnom Penh. Image credit: Spc. Andrew Mendoza/army.mil.