Few, if any, of the commentaries that poured out after the 80th anniversary of Japan’s World War II surrender this month reflected upon Japan’s wartime allies, possibly because most were either a puppet regime or a colony. There was, however, one Asian sovereign state that chose to join Japan, and that was Thailand. The more one looks into the alliance between the two, the less it looks like a forgettable historical footnote.
A Thailand-Japan entente first manifested at a League of Nations’ session in February 1933. There, Thailand (or Siam, as it was known before 1939) diverged from the unanimous condemnation of Japan’s occupation of Manchuria, choosing instead to abstain. Thai sources, notably the memoir of top wartime diplomat Direk Jayanama, explain the straightforwardness behind Thailand’s decision: to avoid antagonizing a rising Japan. Having just gone through a revolution in 1932 that replaced the old absolute monarchy with a constitutional system, Thailand’s domestic politics was fragile, and the new ruling circle wanted to deter any potential foreign intervention. Whatever the reason, the internationally shunned Japan found an ally in Thailand and the two nations shored up bilateral ties.
The Thai-Japanese cooperation expanded markedly in the run-up to the Pacific War, though Thailand strove for neutrality, as evidenced by how it signed non-aggression pacts with Japan as well as with France and Great Britain. Early December 1941 marked the turning point. Almost immediately after Japan’s attack on Pearl Harbor, Japanese troops landed on Thailand’s southern coast and entered from Indochina, demanding passage toward Britain’s Southeast Asian territories. The Thai government yielded quickly to avoid further bloodshed and proceeded to formalize an alliance with Japan by the month’s end. Next came the Free Thai Movement, which collaborated with the Allies against Japan and helped Thailand escape crushing post-war reparations.
The standard textbook summary points to pragmatism and coercion as essential defining features of the Thailand-Japan alliance. But to call Thailand a mere victim of circumstances, joining Japan only to secure its own survival, would be misleading. This overlooks the undercurrent of Thailand’s long-term strategic aspirations and its resolve to pursue them.
The study of Murashima Eiji, a distinguished name in modern Thai historiography, reveals that Thailand, not Japan, was the first nation to develop an early, one-sided interest and reached out first, culminating in the establishment of diplomatic relations through the 1887 Declaration of Amity and Commerce. Even then, Thailand remained the more enthusiastic party, regarding Japan’s Meiji reforms as a successful model of modernization for the Kingdom of Siam. It is important to further note that modernization for Thailand was never just about improving living standards; it was also a direct response to imperialist encroachment from France and Great Britain. For one, Thailand’s first rail line, opened in 1900, was strategically built toward the northeast to assert sovereignty in areas threatened by the expansion of French Indochina.
While Thailand managed to preserve its independence in a region carved up by rival colonial powers, this came at the cost of gradual territorial concessions. Thailand had previously lost lands to Burma and China too, but those were the results of traditional warfare and cannot be viewed in the same category as colonial losses. By 1909, France had snatched parts of Laos and Cambodia over which Thailand had long exercised suzerainty, while Britain absorbed northern Malaya and parts of Myanmar that make up the Shan and Kayah states today, stripping away vast swathes of Thailand’s former domain.
Against this backdrop came Japan’s jaw-dropping victory over Russia in 1905 and its full-fledged revision of unequal treaties with Western powers by the end of the Meiji era in 1912. To Thai elites, this sent a powerful signal. At one level, Japan emerged as an increasingly attractive hedging choice. At a deeper level, the bitterness of territorial losses to Western colonialism had always made Thailand susceptible to the allure of Pan-Asianism.
There were Japanese individuals engaged in Pan-Asianist activities before the term gained widespread currency, and before Tokyo had any defined policy toward Bangkok, as a University of Bristol doctoral thesis by Iida Junzo indicates. When French gunboats threatened Thailand into surrendering the Lao territories in 1893, some Japanese adventurers reacted strongly, reflecting Japan’s own struggles against Western imperialism. They wasted no time in preaching Pan-Asianist resistance. Though small in number, these adventurers made an outsized impact. To quote another historian, Edward Thadeus Flood, “there can be no doubt that at least two high-ranking Siamese nobles in positions of importance in the government lent a very sympathetic ear to these unofficial paladins of Asian solidarity.” More officially, Pan-Asianism found an intellectual face in Inagaki Manjiro, Japan’s first minister to Thailand (1897-1907), whose personal efforts were vital in cementing early Thai-Japanese diplomatic ties.
Had it not been for the accumulation of such sentiments, Thailand would have lacked the confidence to assert its own version of Pan-Thai politics, which it did by the mid-1930s. As a declassified CIA document noted, this had a strong irredentist element, aiming to create “a union of peoples racially or linguistically akin to the Siamese Thais” under Bangkok’s governance. Renaming the country “Thailand” was perhaps the plainest encapsulation of this new vision of pan-Thaism, which also obligated the Thai government to reclaim formerly Thai-controlled territories taken by the Western colonial powers, whether through diplomatic or other means.
Charivat Santaputra’s book on Thai foreign policy from 1932 to 1946 contains some telling stories. That even the prominent liberal reformer Pridi Banomyong, who cautioned against irredentist nationalism and later led the Free Thai, welcomed the retrocession of some territories to Thailand speaks volumes about the colonial legacy’s hold on the Thai psyche. Moreover, then Prime Minister Field Marshal Phibun Songkhram was well aware of the danger of leaning on Japan to further Thailand’s irredentist ambitions. Doing so meant empowering Japanese influence in Southeast Asia and risked compromising Thai neutrality in the wider war, but Phibun considered this the only viable route. The tradeoff was basically acceptable. And the notion that Pan-Asianism, however genuine, was inherently hierarchical under Japanese domination perhaps did not bother Thailand a great deal, provided that its own sub-regional domination was secured and left unchallenged.
So in late 1940, Phibun led Thailand into war with French Indochina. This conflict tends to fly under the radar of mainstream history lessons, given its undeclared and contained nature. The CIA file cited earlier states that Thailand dared to directly challenge France and not Britain because the former, by that point, was a “divided and defeated nation” under the Vichy government. True as it was, Thailand’s grievances with the French ran deeper than those with the British. Not only was the manner in which France took territories more militarily aggressive, but compared to British-occupied areas, French-occupied Cambodia and Laos held more cultural and historical significance for Thailand.
Another thing the CIA file underscores is Japan’s support for Thailand, hinting that the official Thai-Japanese alliance that followed was more or less a natural progression. Indeed, when the Americans halted fighter aircraft deliveries to discourage Thai offensives, Thailand turned to Japan. More importantly, Japan’s mediation in the war with French Indochina allowed Thailand to walk away as the winner in territorial terms: the country regained the three western provinces of Cambodia that it had ceded to France in 1907, and a stretch of Lao territory along the Mekong River that it had been forced to relinquish in 1904. That was Thailand’s first taste of territorial revisionism in modern times, albeit a short-lived one; it was forced to give up these territories after the end of the war.
Aside from spotlighting Thailand’s understated proactivity, the point of this long historical walkthrough is to highlight Japan’s role as an enabler of Thailand’s strategic aspirations. But, of course, this cannot cancel out Japan’s oppressive aspects. Because no single interpretation prevails, Japan’s wartime legacy in Thailand is very much a pendulum, swinging between the poles of liberation and oppression in concert with shifting international currents. Put differently, the malleable duality suggests that the alliance still carries weight in contemporary analysis.
And what of today’s strategic landscape? First, the intensifying U.S.-China competition is coming to dominate international politics, with Thailand and Japan both preferring hedging over decisive alignment. Second, security and defense issues have become more salient, evidenced by the sharp increase in armed conflicts over the past few years. Yet this aspect, as I wrote for The Diplomat three years ago, has been the weakest link in postwar Thailand-Japan relations. Third, Thailand and Japan are similarly constrained by structural problems: rapidly ageing populations, economic troubles, immigration challenges, and political instability (although the latter is obviously more entrenched and severe in Thailand). These leave neither country able to afford expansive conquest as in old times.
Building on that second point, Thailand has made headlines in recent months for clashing with Cambodia over a disputed border, itself a product of ambiguous French colonial cartography. This dispute has inevitably stirred up nostalgia for Thailand’s irredentist gains of the early 1940s, effectively swinging perceptions of Japan’s wartime legacy toward the role of liberator. Thais already view Japan in one of the friendliest lights of any nation, and if that favorable perception extends into the realm of defense, it leaves the door open wide for deeper cooperation on shared interests like maritime security. The tricky business is to keep the favorable sentiment from being spun into Japan siding with Thailand against Cambodia. That won’t happen and would only work against Thailand’s interest in keeping the border conflict localized.
In short, the ingredients are all there for a stronger Thai-Japanese defense engagement. Thailand’s designation as a recipient of non-lethal defense equipment from Japan as part of its Official Security Assistance initiative evidently signals an upward trajectory. At the same time, Thailand and Japan are operating in an international arena fraught with complex, emotionally-driven conflicts and misinformation. To prevent their partnership from being weaponized, growing defense cooperation must go hand in hand with effective communication.