World War II : The history of Thailand from 1932 to 1973

In 1940 most of France was occupied by Nazi Germany, and Phibun immediately set out to avenge Siam's humiliations by France in 1893 and 1904 when the French limited the borders of Siam to the north by forcing a series of treaties. Luang Wichit wrote a number of popular dramas that glorified the idea of many ethnic groups belonging to one greater "Thai" empire and condemned the evils of European colonial rule. Irredentist and anti-French demonstrations were incessantly held around Bangkok, and in late 1940 border skirmishes erupted along the Mekong frontier. In 1941, the skirmishes became a small scale war between Vichy France and Thailand. The Thai forces dominated the war on the ground and in the air, but suffered a crushing naval defeat at the battle of Koh Chang. The Japanese then stepped in to mediate the conflict. The final settlement thus gave back to Thailand a number of the disputed areas in Laos and Cambodia.

Phibun's prestige was so increased that he was able to bask in a feeling of being truly the nation's leader. As if to celebrate the occasion, he promoted himself to field marshal, skipping the ranks of lieutenant general and general.
This caused a rapid deterioration of relations with the United States and Britain. In April 1941 the United States cut off petroleum supplies to Thailand. Thailand's campaign for territorial expansion came to an end on December 8, 1941 when Japan invaded the country along its southern coastline. The Phibun regime allowed the Japanese to pass through the country in order to attack Burma and invade Malaya. Convinced by the Allied defeats of early 1942 that Japan was winning the war, Phibun decide to form an actual military alliance with the Japanese.
As a reward, Japan allowed Thailand to invade and annex the Shan States in northern Burma, and to resume sovereignty over the sultanates of northern Malaya which had previously been taken away in a treaty with Britain. In January 1942 Thailand actually declared war on Britain and the United States, but the Thai Ambassador in Washington, Seni Pramoj refused to deliver it to the State Department. Instead, Seni denounced the regime as illegal and formed a Seri Thai Movement in Washington. Pridi, by now serving in the role of an apparently powerless regent, led the resistance movement inside Thailand, while Queen Ramphaiphanni was the nominal head of the movement in Great Britain.

Secret training camps were set up, the majority of them by the populist politician Tiang Sirikhanth in the northeast of the country. There were a dozen camps alone in Sakhon Nakhon Province. Secret airfields also appeared in the northeast, where Royal Air Force and United States Army Air Force planes brought in supplies, as well as Special Operations Executive, Office of Strategic Services, and Seri Thai agents; while at the same time evacuating out prisoners of war. By early 1945, Thai air force officers were performing liaison duties with South East Asia Command in Kandy and Calcutta.

By 1944 it was evident that the Japanese were going to lose the war, and their behaviour in Thailand had become increasingly arrogant. Bangkok also suffered heavily from the Allied bombing raids. This, plus the economic hardship caused by the loss of Thailand's rice export markets, made both the war and Phibun's regime very unpopular, and in July Phibun was ousted by the Seri Thai-infiltrated government. The National Assembly reconvened and appointed the liberal lawyer Khuang Aphaiwong as Prime Minister. The new government hastily evacuated the British territories that Phibun had occupied and surreptitiously aided the Seri Thai movement while at the same time maintained friendly relations with the Japanese.
The Japanese surrendered on August 15, 1945. Immediately the Allied military responsibility for Thailand fell to the British. As soon as practicable, British troops were flown in and these rapidly secured the release of surviving POWs. The British were surprised to find that the disarmament of the Japanese soldiers had already been largely completed by the Thais.

The British regarded Thailand as having been partly responsible for the immeasurable damage dealt upon the Allied cause and favoured treating the kingdom as a defeated enemy, but the Americans had no great sympathy for British and French colonialism and decided to support the new government. Thailand thus received little punishment for its wartime role.

References :1932: Revolution in Siam by Charnvit Kasetsiri; Thammasart University Press, 2000 The End of the Absolute Monarchy in Siam by Benjamin A. Batson; Oxford University Press, 1984 History of the Thai Revolution by Thawatt Mokarapong; Thai Watana Panich Press, 1983 The Free Thai Legend by Dr. Vichitvong na Pombhejara; Saengdao, 2003 · Siam becomes Thailand by Judith A. Stowe; University of Hawaii Press, 1991 · Thailand: A Short History by David K. Wyatt; Yale University Press, 2004 · Thailand: The Politics of Despotic Paternalism by Thak Chaloemtiarana; Thammasart University Press, 1979 · Thailand's Secret War: OSS, SOE and the Free Thai Underground During World War II by E. Bruce Reynolds; Cambridge University Press, 2004