Good Neighbors Make Good Fences: The Strategic Basis for a Thai-Vietnamese Entente

The encroachment by Cambodian troops into the disputed areas along the country’s border with Thailand around the “Emerald Triangle,” resulting in an exchange of fire and the death of a Cambodian soldier in late May, has added to Thailand’s growing two-front insecurity. Besides the emotionally charged nationalist tensions with Cambodia over the question of territorial sovereignty on the eastern border, the threat of spillover from Myanmar’s bloody civil war on the western front has become a new normal.

Despite Thailand’s clear superiority in material capabilities, the time and energy needed to deal with these immediate neighbors simultaneously can be deeply draining. As such, easing pressure on one border to focus on the other would benefit Thailand in the long run, and Vietnam – with its own dual-front dilemma and parallel interests in preserving Indochina’s strategic balance – is a logical partner in that effort.

If the relationship between the United States and China is what sets the global tempo, then the dynamics between Thailand and Vietnam have long shaped the trajectory of the mainland Southeast Asian subregion. As the two dominant powers in mainland Southeast Asia, Thailand (Siam) and Vietnam (Annam) have often vied for influence over Laos and Cambodia, which both countries saw as lying within their respective spheres of influence. That historical rivalry culminated in the Siam-Annam joint suzerainty over Cambodia in 1845, which turned Cambodia into a buffer state for both, after they could not settle the question by force.

When France began its colonization of Indochina in the 1850s, the historical rivalry became a Siamese-Franco conflict. France fought Siam in 1893 to force the handover of Luang Prabang and other areas to France-controlled Laos. In 1887, 17 years after extending a protectorate over Cambodia, France incorporated the country into French Indochina, thus gradually allowing Vietnamese officials to dominate levels of the colonial bureaucracy in Cambodia, and later in Laos, under French tutelage. It was this logic of geographical and political dominance over Laos and Cambodia that inspired many Vietnamese communists to fight for Vietnam’s independence under the banner of the Indochinese Communist Party. Later, the Democratic Republic of Vietnam and the post-1976 Socialist Republic of Vietnam integrated both Laos and Cambodia into one single battlefield during the war of independence against France, the war of unification against the United States, and the war of border defense against China in a bid to increase Vietnam’s strategic depth. To many Vietnamese leaders, Laos and Cambodia have been central to their survival.

Vietnam’s use of Laos and Cambodia for its revolutionary and security objectives during the three Indochina Wars raised fears in Thailand, which, beginning in 1951, adopted an anti-communist policy with material support from the United States. In 1954, after the end of the First Indochina War, Thailand and the United States became treaty allies. North Vietnam’s use of the Ho Chi Minh Trail to liberate the South, its military presence in Laos and Cambodia, and its vocal support for the Communist Party of Thailand quickly turned the historical rivalry between Thailand and Vietnam into a proxy war between the United States and the communist bloc. Thailand sent troops to South Vietnam and served as a military base for the United States to bomb North Vietnam. The fall of Indochina under communist rule during the course of 1975 led to massive fears in Thailand that the country would be the next domino to fall.

Intra-communist conflicts between Vietnam and China as well as Vietnam and the Khmer Rouge ended post-Vietnam War Thailand-Vietnam attempts to normalize ties, as Thailand saw Vietnam’s invasion and occupation of Cambodia in 1978-1979 as a threat to its security. Thailand aligned with China and the United States to support the Khmer Rouge’s resistance against Vietnam; while Hanoi sided with the Soviet Union to defend itself against the China-Khmer Rouge-Thailand alliance. The Thailand-Vietnam rivalry now became a proxy of the Sino-Soviet Split. Still, despite being the frontline states to many great-power competitions, the Thailand-Vietnam rivalry, starting before the onset of Western imperialism, demonstrated that both Bangkok and Hanoi exercised their own agency to protect their respective living space. Great power allies were to supplement, not to replace, the Thailand-Vietnam rivalry over Laos and Cambodia.

The conclusion of the Third Indochina War in 1991 turned the page on the relationship from confrontation to cooperation. Political momentum in the immediate aftermath of the Cold War was strong as both Thailand and Vietnam endeavored to reorient their foreign policies toward greater non-alignment and regionalism. After Thailand and Vietnam successfully resolved their differences on land with a diplomatic settlement of the Cambodian question and the mutual fear of a Vietnamese invasion of Thailand or a Thailand-backed anti-communist insurgent invasion of Vietnam dissipated, they began to settle their disputes at sea. One noteworthy success came in 1997, shortly after Vietnam’s 1995 entry into ASEAN, in the form of a maritime boundary agreement. Up until that point, no pair of coastal states along the geographically complex Gulf of Thailand had managed to end their maritime disputes bilaterally and in all aspects. Yet Thailand and Vietnam did, delimiting all their maritime zones, including the usually much-disputed continental shelf and Exclusive Economic Zone. The post-1991 rapprochement demonstrated that Bangkok and Hanoi are willing to put aside their rivalry in the service of regional stability.

The establishment of a Thailand-Vietnam strategic partnership in 2013, and the recent elevation of the relationship to a Comprehensive Strategic Partnership (CSP) – the highest tier in Vietnam’s diplomatic classifications – represent the continuation of the post-Cold War Thailand-Vietnam rapprochement. True to their shared diplomatic spirit of neutrality, the Thai-Vietnamese CSP as it stands is vague on traditional security involving great power politics. Strong emphasis is placed on transnational nontraditional security concerns: fighting drugs, scammers, human trafficking, and illegal, unreported, and unregulated (IUU) fishing. But quietly looming behind the CSP’s polite language is a mutual unease about China’s expanding land and naval presence in the subregion.

The current convergence between Thailand and Vietnam centers most concretely on China’s activities in Cambodia and Laos. With respect to Cambodia, China is boosting its political clout via the modernized Ream Naval Base and the Funan Techo Canal. Concerns go beyond diminishing Thai and Vietnamese trade influence. The potential for these projects to serve military ends during wartime would severely limit Thailand and Vietnam’s operational maneuverability, making non-alignment practically impossible to sustain because China will pose too much of a threat for either of these countries to confront China alone. In addition to the growing Chinese presence in Cambodia, China’s ambitious investments in Laos and Vientiane’s growing debt to Beijing also increase the risks of Laos falling into a Chinese debt trap, under which it may lease strategic assets to China as compensation. With Laos sharing a long land border with both Thailand and Vietnam and being a battlefield between ancient Thai and Vietnamese kingdoms, China’s footprint in Laos is as concerning to Thailand and Vietnam as its footprint in Cambodia. Welcoming China to Indochina is one thing; accepting an overwhelmingly Chinese-dominated Indochina is another. This is something that is not in the interest of either Thailand or Vietnam.

Vietnam knows that it cannot outbid China to win Lao or Cambodian loyalty due to the massive power imbalance vis-à-vis Beijing. At the same time, a painful memory of China’s punishment the last time Vietnam tried to dominate its western neighbors by force between 1978 and 1991 has cautioned Vietnam against going down the same path, even when the strategic importance of Laos and Cambodia to Vietnam’s security remains paramount. With Vietnam now effectively encircled by China on both the continental and the maritime fronts, it has an interest in fostering a closer partnership with Thailand to stabilize its continental domain in service of its pivot toward the maritime domain. In the Vietnamese psyche, Thailand represents the limit to Vietnam’s western expansion in much the same way that China forms the northern barrier. Laos and Cambodia, being inherently weak, can only pose a threat to Vietnam if they are backed by either China or Thailand. But unlike the recent past, Thailand now shares Vietnam’s concern over Chinese behavior, even if it hesitates to say so out loud.

Fortunately for Vietnam, the prospect of a meaningful China-Thailand alliance is unlikely despite their growing military cooperation. This is because China is also a fixed element in Thailand’s two-front security challenge. In Myanmar, most of the Chinese-backed ethnic armed organizations are ones that Thailand regards as unfriendly, if not outright threatening. The most prominent of these is the United Wa State Army, which has made increasingly bold incursions near the northern Thai border in a bid to expand its territorial control.

When it comes to the Cambodia-Thailand conflict, China’s professed neutrality is viewed by Thais with suspicion. The friendly ties China shares with both sides cannot defy the reality that its relationship with Cambodia is much more entrenched and strategically aligned than its relationship with Thailand, a reluctant yet still formal U.S. security ally. With China serving as Cambodia’s primary source of military aid, training, and equipment, it makes sense for the Thais to see a link between Chinese support and Cambodia’s growing confidence in asserting its territorial claims. The massive Cambodian-Chinese joint exercise under the Golden Dragon series, right before the latest Thai-Cambodian border flare-up, only added fuel to that perception.

While China’s presence in Laos may not pose a conventional military threat, it still puts Thailand’s sovereignty at risk. Laos’ special economic zones along the Thai border, where China has outpaced all other foreign investors and governance is notoriously weak, have already seen Chinese security personnel deployed to maintain order. In light of the current boom of transnational scam operations, China could entrench itself under the pretext of protecting its citizens, leaving Thailand struggling to resist.

Since the Cold War, the Thailand-Vietnam relationship has been on an upward trajectory, something that is poised to continue due to a shared concern over China’s presence in Indochina. A quiet show of Thai-Vietnamese unity, such as through enhanced surveillance cooperation, joint patrols, or coordinated diplomatic messaging, is encouraged not to directly provoke China, but to apply subtle pressure on Cambodia and Laos to make their development decisions more transparent and accountable to Thailand and Vietnam’s security interests. Importantly, the nature of this kind of cooperation will be non-rivalrous, which should address the structural skepticism that Bangkok and Hanoi still have over one another’s intentions regarding Laos and Cambodia.

At the same time, Thailand and Vietnam should adopt the same policy toward China: that is, to reassure China of their peaceful intentions regarding Laos and Cambodia by enhancing regional cooperation with Beijing over areas such as the Mekong River, infrastructural connectivity, or climate change. Bangkok and Hanoi should also commit to de facto neutrality by not allowing any extra-regional powers to use their territories to hurt Chinese interests. For both Thailand and Vietnam, maintaining an amicable relationship with China is the foundation of a successful policy toward Laos and Cambodia. It is not a coincidence that Thailand’s and Vietnam’s respective ties with China are in general improving, even when they share concerns about Chinese behavior.

A Thailand-Vietnam entente over Laos and Cambodia would give them more space to address their respective two-front dilemma. For Thailand, that means redirecting attention to the western flank with Myanmar, where a long, porous frontier, more armed actors, and refugee flows demand greater focus than the border with Cambodia. Vietnam, for its part, would be better positioned to pivot eastward to the South China Sea, where a naval modernization and island reclamation campaign will be essential to developing its maritime economy. In the grand scheme of things, Thailand and Vietnam can complement one another’s security by keeping mainland Southeast Asia a zone free of great-power competition and political instability.