During WW2, Thailand "fought" Japan for a single day then "surrendered" and became an Axis country freely trading with Japan and far away Germany. Thai people actually suffered more casualties being bombed

by the US and Britain afterwards.

Thailand's borders actually expanded during WW2 as their Japanese allies gave them chunks of defeated France's colonies, such as Laos. The French colonial governor of Laos, Jean Decoux, attempted to rally his subjects against Thailand and Japan but found little success. When Japan was defeated, Laotian freedom fighters declared independence but found their long struggle yet to end with France's colonial return.

There's even a famous Thai drama, Khu Kam, about the forbidden love between a Thai woman that's the daughter of a pro-American politician and a young Japanese navy officer sent to Thailand:

Also adopted into film as Sunset at Chaophraya (1996 film)

...and popular enough to get remade again Sunset at Chaophraya (2013 film)

Thai history books today pay lip service to the US in denouncing the Axis, but the Thai people don't have any strongly negative impression of anyone (the land of smiles indeed). If anything a larger negative impact on the country was when the Vietnam war occurred and Western forces poured in for prostitution at an unheard of scale. Imperial Japan's impact in Thailand is largely forgotten in comparison. While some western journalists tried to justify their part in the sex trade as the modernizing of backwards nations...

I couldn’t help wondering just how long all the neon-lighted prosperity of Bangkok would last after a settlement of the Vietnam War: a large section of the Thai economy is geared to the demands created by the war, and in particular to the more basic demands made by the thousands of American military personnel on “R and R.” (euphemism for prostitution)
-Traveller’s Tales, Far Eastern Economic Review 27 July 1967, 187.

...champions of humanity like Martin Luther King Jr. saw it as an abhorrent assault on foreign nations:

"Children are compelled to sell their sisters our soldiers... we have corrupted their [Vietnamese] women and children… what
-Sevy, The American Experience in Vietnam, 229

As for Vietnam, they were also French colony at the time. When France was defeated by Germany, French-Vietnam fell under Japanese control with occasional conflict with French colonial troops. Any Vietnamese who was pro-independence fought against France and Japan equally, and when Japan was defeated France returned as the tyrants to overthrow.

Vietnam would suffer far more from the Vietnam war which saw rape, forced prostitution and slaughter of civilians on a massive scale that overshadowed the crimes Imperial Japan had inflicted in their brief time of rule. Despite that history though Vietnamese today are very friendly towards Americans and other foreigners. Vietnamese are pretty much the worst people in the world at holding grudges.

With Indonesia, they were a Dutch colony at the time. The Japanese were initially welcomed as liberators from colonial servitude and many Indonesians joined in driving out the Dutch.

"With the arrival of the Japanese just about everyone was full of hope, except for those who had worked in the service of the Dutch."
-Pramoedya Ananta Toer, Indonesian writer at the time of WW2

Though war time rationing and increasingly harsh style of government under Japan quickly showed that they were yet another colonial master and thousands would perish under forced labor and political purges. When Japan was defeated and the Dutch (with the help of Britain) tried to re-instate colonial control, they found that the infrastructure and government structure left over by Imperial Japan had united the now independent Indonesian people into an efficient fighting force. After a few years of fighting the Dutch and British saw their imperialistic ambitions dashed for good.

To Indonesians, hatred of Japan for WW2 does not stand out among the centuries of accumulated hatred for European invaders, who today they don't hold much resentment for either. A similar story is told of Malaysia, but I'm not as familiar with their history to say much more about it.

With all that being said something else comes to mind...

Territorial disputes, or the lack of them with Japan

The countries I've talked about don't have any huge territorial disputes with Japan. But the countries that are most outraged by Yasukuni shrine visits do. Looking at the People's Republic of China in particular the anger over the honoring of war criminals goes hand in hand with public attention on territorial disputes.

Now it's Imperial Japan's war time victim, China, that is in territorial dispute with various Southeast Asian countries. So even though the Philippines and China were both on the same side during WW2 today you see the Philippines doing naval exercises with Japan in fear of Chinese aggression.

PH, Japan, US conduct naval exercises off West PH Sea

Wartime history is interesting to delve into, but it's ultimately modern geo-political maneuvering that influences how much one nation's people despises the other.

The optimist in me sees that as "even enemies can become friends if conditions change", but the pessimist then interjects "...and so allies can become enemies".

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