In Search of Thailand’s Strategy: ASEAN and the Thai-Cambodia Question

The “Guns of July”—regardless of who fired the first shot—may have shattered any real immediate chance for Thailand and Cambodia to resolve their long-running border dispute through diplomacy. Nationalism and antagonism have intensified the conflict, leaving the already fragile relationship between the two countries under severe strain. As the region searches for solutions, criticism of ASEAN’s handling of the situation has also been a feature.

The conflict escalated when three Thai soldiers were injured by a landmine explosion in the Chong Bok area, prompting Thailand to recall its ambassador to Cambodia. The resulting downgrade in diplomatic relations led to the closure of the border and armed clashes that left dozens dead and caused civilian casualties.

Cambodia submitted a complaint to the United Nations Security Council, citing Thailand as the aggressor, while Thailand countered with accusations that Cambodia had violated international humanitarian law, including attacks on civilian areas such as Phanom Dong Rak Hospital.

While land border disputes dominate the current headlines, overlapping maritime claims in the Gulf of Thailand also pose serious and underexplored challenges. These tensions should not be viewed in isolation but as part of a broader geopolitical package.

Amid the rising strain, questions have been raised about ASEAN’s effectiveness, despite Malaysia, as ASEAN Chair, successfully mediating a peace agreement over the last few days that ended the latest border violence.

Thailand’s Maritime Security Outlook

Located at the heart of mainland Southeast Asia, Thailand historically places greater emphasis on land-based threats than maritime ones. The 20-year National Security Strategy (2018–2037) ranks “maintaining maritime security and safeguarding national interests at sea” only fourth among 17 key priorities. The top priorities are the protection of core institutions, particularly the monarchy, sovereignty, and border stability.

Supporting this hierarchy, the National Security Council ranked maritime security just 7th out of 28 national security concerns. This prioritisation is reflected in the relatively subdued role maritime threats play in Thai defence policy. The National Strategy for Maritime Security (2023–2027) identifies key flashpoints—including the South China Sea, Strait of Malacca, Taiwan Strait, and Gulf of Oman—but these issues remain subordinate to traditional security concerns.

Maritime Disputes with Cambodia

Thailand and Cambodia's maritime disputes are closely tied to their broader tensions. The overlapping maritime claims in the Gulf of Thailand—an area of over 280,000 sq km bordered by Malaysia, Thailand, Cambodia, and Vietnam—remain unresolved due to conflicting claims over Exclusive Economic Zones (EEZs), compounded by the Gulf’s narrow width.

Both countries declared continental shelf boundaries in the early 1970s, with Cambodia’s declaration in 1972 and Thailand’s in 1973. The resulting overlap spans more than 26,000 sq km, delaying petroleum exploration and complicating bilateral cooperation despite private concessions issued by both governments.

Efforts to resume talks in early 2024 were derailed after the Constitutional Court removed Prime Minister Srettha Thavisin from office. The hope that Thaksin Shinawatra's long-standing personal ties with Hun Sen might ease the current tensions has been dashed. With relations between the Shinawatra and Hun families deteriorating, nationalist rhetoric has escalated, raising the political temperature around disputed areas such as Koh Kut—a Thai island partially claimed by Cambodia.

The Thai-Cambodia border crossing at Aranyaprathet, 240 kilometres east of Bangkok / image Thanate Tan Flickr CC

ASEAN as Strategic Anchor

Given the stalemate, the current conflict should serve as a wake-up call for Thailand to elevate maritime security in national policy discussions. It also offers ASEAN an opportunity to reassert its relevance. Although far from perfect, ASEAN arguably remains Thailand’s most viable platform for regional engagement—particularly as the Gulf of Thailand dispute risks being overshadowed by broader regional instability.

Thailand's National Maritime Security Strategy (2023–2027), suggests ASEAN mechanisms such as the ASEAN Maritime Forum (AMF), the ASEAN Regional Forum (ARF), the Inter-sessional Meeting on Maritime Security (ISM), and ASEAN Defence Ministers’ Meetings (ADMM and ADMM-Plus) should be leveraged to address maritime security challenges. Likewise, the ASEAN Ministerial Meeting on Transnational Crime (AMMTC) can play a supporting role.

Thailand could also pursue operational coordination measures, including joint patrols, maritime surveillance, information and technology sharing, and intelligence networks. These can foster trust and enable incremental gains in cooperation. Issues such as piracy, illegal immigration, and human trafficking could be better addressed through such collaboration, enhancing regional resilience and confidence.

ASEAN Centrality: Still the Only Game in Town

While ASEAN faces growing criticism—particularly for its informal, non-binding structure—it still plays a critical role in preventing conflicts from escalating into full-scale war. Track 1.5 and Track 2 diplomacy, particularly within academic and civil society spheres, can help the public better understand ASEAN’s nature and limits.

July 28, 2025: Cambodian PM Hun Manet and Thai Acting PM Phumtham Wechayachai agree to ceasefire during Malaysia peace talks chaired by ASEAN Chair PM Anwar. Image: Hun Manet/Facebook

Amid the nationalist fervour undermining Thai-Cambodian ties, the ASEAN-centric approach remains Thailand’s best strategic bet. Opting for international arbitration, particularly through the International Court of Justice (ICJ), could backfire, as Cambodia has demonstrated greater proficiency in navigating international legal forums.

Thailand must focus on capacity-building efforts with ASEAN and external partners to ensure its strategy is effective. Even amid domestic political crises, ASEAN offers the most practical pathway for regional stability—certainly more so than reliance on external actors like China, Japan, South Korea, or the EU.

A Test of Regional Resilience

The aftermath of the "Guns of July" will likely define a new phase in Thai-Cambodian relations and test the resilience of ASEAN as a regional institution. As the region continues to grapple with internal tensions and external pressures, Thailand’s ability to navigate its disputes through ASEAN will play a pivotal role—not just in bilateral relations but in the shaping of Southeast Asia’s future security landscape.

• The opinions expressed are those of the author

Asia Media Centre