Why didn't Thailand have to pay more for its involvement in WW2?

Question

During WW2, Thailand declared war on England and US, collaborated with the Japanese in exchange for being able to invade Shan state westwards and north as far as China. Thai soldiers were ordered to fight alongside with Japanese in Malaya and Burma. Thailand was at least "allied with the axis".

After the war they just had to give back the territory and some bags of rice I think.

How come they were let off the hook so easily? Why didn't the allies go harder on their (former) enemy Thailand?

And also the leader Phibun just resigned. (To compare Quisling was shot.) (Personally I would just say that Buddhist mentality does not have death penalty as an easy option.)

My account of the history is highly simplified and may be wrong in some parts. I am a traveler and have seen these areas first hand and heard the stories, so therefore I am interested. I am no historian, I hope possible faults in my account will be corrected.

Answer 1

One country that wasn't forced to pay "a lot" for joining the Axis in World War II was Finland. Thailand was probably viewed in much the same way.

Putting Germany and Japan aside, the third country that was considered part of the "core" Axis was Italy. That's probably because Italy by itself started a lot of wars in other countries; it attacked Abysinnia (Ethiopia) in 1934; it conquered Albania and attacked Greece in 1939; it attacked Egypt from Libya in 1940; it "stabbed France in the back" in 1940. Basically, Italy acted much like the two larger Axis nations in initiating conflicts, including some that were unwelcome to its German ally.

Thailand, like Finland, was more like a "fellow traveler" with the Axis than a true ally. Like Finland, it won some favorable "border adjustments" in exchange for some "cooperation." But apart from that, Thailand didn't do much against third parties and kept pretty much to itself during the war. Also, Thailand (and Finland) had a record of "non-aggression," so its actions during World War II were considered to taken out of necessity; that is, "eat or be eaten."

Note that America dealt more leniently with Thailand and Finland than some other Allies, but America was the most powerful one. Unlike the case of Finland (and Balkan countries such as Romania and Bulgaria), the Soviet Union was not part of Allied dealings with Thailand.

Answer 2

Question can be trivially answered through Wikipedia.

"Thailand officially adopted a position of neutrality until it was invaded by Japan in December 1941."

"Moreover, the post-war accommodations with the Allies weakened the civilian government. As a result of the contributions made to the Allied war efforts by the Free Thai Movement, the United States, which unlike the other Allies had never officially been at war with Thailand, refrained from dealing with Thailand as an enemy country in post-war peace negotiations" Wikipedia

The referenced article contains more information and nuance.