A Question of National Sovereignty – Relations between Thailand & Japan on the eve of World War II

Japanese troops in Bangkok

The military faction around the Thai Prime Minister, Marshal Phibun Songkhram, had maintained close and excellent relations with Japanese officials since the 1932 coup. Logical, because they shared a number of common interests.

This handout was striking, because since the reign of King Chulalongkorn (1868-1910), Siam has watched over the strictest possible neutrality in foreign relations. This new orientation, aimed at rapprochement between the two nations, was first dramatically emphasized in 1933. When a motion against the Japanese invasion of Manchuria was voted in the League of Nations, Siam was the only member state to abstain. The Japanese-Thai advances became even more apparent in the period between 1933 and 1938 when the Siamese government, under pressure from the military, invested heavily in an ambitious armaments program designed to modernize the Siamese armed forces. The army was expanded to 33 infantry battalions and, in addition to three new artillery units, also received an armored division. Much of the new material came directly from Japanese arms factories. The Japanese imprint on the expansion of the much-aged Thai navy was even more spectacular. As many as 16 of the 24 new Siamese warships rolled off the slipway in Japanese shipyards…

Although these purchases showed a clear preference for Japan, this did not automatically mean that the Phibun government completely sided with Japan. Thailand was still scrupulously trying to maintain a policy of strict neutrality. Faced with the unrelenting threat of war, Phibun tried unsuccessfully to gain insight into Japan's intentions towards Thailand. At the same time, he sought guarantees from Britain and the United States for military and financial support should Thai neutrality be violated by a Japanese invasion. However, Bangkok was distrusted by both camps. Britain and the United States viewed Thailand as an ally of Japan due to Phibun's personal authoritarian leanings as well as Thailand's own irredentist grievances over border disputes with French Indochina. While Tokyo put the biggest question marks at the outspoken pro-Western elements in the Thai cabinet.

Japanese Chi Ro tanks in the Thai army

In August 1939, a few days before the German invasion of Poland, Paul Lépissier, the French chargé d'affaires in Bangkok, contacted Phibun with the proposal to conclude a Non-Aggression Pact with his country. An initiative that was prompted precisely by the French suspicion of the revanchist Thai prime minister, who had long since rejected the idea of ​​the Mekong as a natural state border. The Thai government was sympathetic to this proposal, but believed that a similar treaty should also be concluded with Great Britain, which could also be regarded as a neighboring country through its colonies. A perfectly defensible course of action from a diplomatic point of view. To the astonishment of France and Great Britain, Phibun then also asked Japan to the negotiating table. The Thai government hid behind a vague statement about Japan's role in the region to justify this unusual diplomatic initiative.

In May-June 1940, when the German army brought France to its knees, Germany's ally Japan saw an opportunity to gain control of French Indochina. At the same time, ties with Bangkok were strengthened. In June 1940, Japanese and Thai diplomats in Tokyo had reached an agreement on a Treaty of Friendship that would not be signed until December 23, 1940 in Bangkok.

However, almost simultaneously and in anticipation of a possible Japanese invasion, the pre-war Thai government had made several official requests to the British for help. On August 31, 1940, at a time when the Battle of Britain was at its dramatic climax, the British and Thai governments officially signed an Anglo-Thai Non-Aggression Pact in Bangkok. However, the British would soon question the attitude of the Thai cabinet in general and Prime Minister Phibun in particular.

Phibun decorates Thai pilot who shot down a French plane

Japanese troops were active in Southeast Asia from the late summer of 1940. With the permission of the French Vichy regime, Emperor Hirohito's troops were allowed to remain in what is now North Vietnam and possibly even to operate in the entire territory of Indochina. Not averse to some opportunism, Phibun Songkhram had already taken advantage of the German invasion of France and subsequent French capitulation in the same late summer of 1940 to militarily to re-annex large tracts of territory east of the Mekong, which Siam had unwillingly handed over to the French at the end of the nineteenth century as a result of the gunboat diplomacy of the French in the First Franco-Siamese War (1895) . And again Japan came to the fore as it was aboard the Japanese warship Natori that on January 31, 1941, an armistice was concluded in Saigon Bay between Vichy France and Thailand… The final peace agreement between the two parties was signed on May 9, 1941 in… Tokyo.

This drastic action was certainly not well received in the West. The Americans in particular regarded this action as an act of aggression in favor of Japan. President Roosevelt even stated, without sarcasm, that if Japan attacked Thailand no one would know if the Japanese had not been invited to do so by some secret arrangement between Tokyo and Bangkok…. That is why he insisted that no single Western nation should give guarantees to protect Thai sovereignty. On October 9, 1940, fearing an escalating Indochina conflict, the Americans had already blocked a Thai order for 10 dive bombers, while Bangkok had already paid for these aircraft. Incidentally, the US would threaten to turn off the oil tap a few months later in response to the growing Japanese influence on Thailand. After all, there were only two major petroleum distributors in Thailand: the British/Dutch Royal Dutch Shell and the American Standard Vacuum Oil Company.

Meanwhile, the Imperial Grand Headquarters in Tokyo decided on July 2, 1941 to advance towards South Vietnam with the intention of building a number of bases there that could be useful in the major offensive planned for early December in the region. At the same meeting, it was also proposed to attack Thailand to end what was described as "British intrigue in Bangkok'. At the time, Japan was involved in a trade war with Great Britain over Thai rubber and tin production. But the plan to invade Thailand immediately met with internal resistance and was eventually shelved.

While the Japanese now became active in almost all of Indochina, and considerably strengthened their troops in the region, tensions rose. It was not only in Bangkok that serious consideration was now being given to a Japanese offensive in Southeast Asia. On August 6, 1941, U.S. Secretary of State Cordell Hull declared that an act of Japanese aggression against Thailand would be regarded by Washington as a threat to U.S. security in the Pacific. A rather woolly statement that was symptomatic of the mistrust that Washington still displayed towards Bangkok. That same day, Anthony Eden, the British Foreign Secretary, made it clear in much stronger terms that a Japanese attack on Thailand would have dire consequences. But the British, weakened by the Battle of Britain and the relentless bombardments of the Blitz and, moreover, having had the greatest difficulty reorganizing their forces after Dunkirk, had much more to lose in the Far East than the Yankees. Burma and Malaysia, two neighboring countries of Thailand, were British crown colonies, not to mention the strategically important colony of Singapore… Winston Churchill swore to the Thai government that it would stand its ground in the event of Japanese aggression, but concrete help could not he, apart from a delivery of a load of artillery shells and a few howitzers, barely offer.

Until mid-November 1941, the Imperial Headquarters in Tokyo were still of the opinion that it would suffice to simply ask Bangkok for permission to allow free passage for the Japanese troops on their way to Burma and Malaysia. The Japanese secretly hoped that the British would station preventive troops in Thailand before this would actually happen. This British military presence would give Tokyo a pretext for an invasion of Thailand. But the British did not fall into this overly transparent trap. Winston Churchill, disturbed by his intelligence reports of an imminent Japanese invasion, thought it useful to press Roosevelt again, this time more forcefully, for support. He did this on December 7, 1941, a few hours before the Japanese attack on Pearl Harbor…

On December 8, 1941, due to the time difference almost simultaneously with the attack on Pearl Harbor, the Imperial Japanese Army invaded Thailand simultaneously in nine places: by land at Battambang in Cambodia, by air at Dong Muang airport in Bangkok, and by sea with seven amphibious landings between Hua Hin and Pattani on Thailand's Gulf Coast. Barely a few hours after the Japanese invasion, the Thai government – ​​despite fierce fighting back in places – decided to lay down its arms, realizing that no British aid would come and believing that further resistance to the numerical stronger and better armed Japanese would be suicide. The rest is history…