‘THAILAND AND THE STRUGGLE FOR SOUTHEAST ASIA’ by Donald E. Nuechterlein. Published by Cornell University Press 1965
The final step that Thailand took to align itself firmly with Japan came on January 25, 1942, when it declared war on Great Britain and the United States.
The reason given for this action was that the participation of British and American fliers in bombing attacks against civilians as well as military targets in Thailand constituted an act of aggression.
Britain was also accused of economic manipulation of the national economy to the detriment of Thailand; and the United States was accused of refusing to deliver airplanes, previously paid for by Thailand, and of having failed to come to Siam’s assistance by 1893 when it was threatened by France.
Sir Joseph Crosby observed that the communique issued by the Thai government ‘can only be held to have set up a record for childish insincerity which must be wellnigh unique in the history of international relationships, and future generations of Siamese will assuredly blush to recall it.’
From that time on until 1944, Thailand cooperated fully with Japan, and during the war the two countries exchanged many missions of good will. Thailand retained nominal control of its internal administration; but Japan made ever greater demands on its economy, inflicting considerable economic hardship on the country before the war’s end.