If you believe certain sources, look at some of the rest of these:
countrystudies.us/thailand/21.htm
en.wikipedia.org/wiki/History_of_Thailand_(1932%E2%80%931973)
www.countriesquest.com/asia/thailand/history/world_war_ii.htm
www.mofa.go.jp/region/asia-paci/thailand/index.html

Thailand was invaded along its southern peninsula, and after a brief fight by local police, ceased hostilities and signed an alliance agreement with Japan.

Led by Field Marshall Phibunsongkram, Thailand eventually fully embraced the alliance when things went well for the Japanese. Its military fully cooperated with the Japanese in the invasion of Burma via Thailand.

After the war, the British wanted to treat Thailand as a conquered enemy, but the US stopped that due in part to already rising concerns over the Cold War.

With the help of the US CIA, a personality cult around the king was given even greater support to bind the country together in the face of the communist threat.

The CIA and the king then actively supported a string of military dictators, setting in motion trends and events that are still being felt today.