No doubt. the Thai played smart and remained the only country in SE Asia that was not colonized.
back then Vietnam made the major mistake by following Chinese model of closed door policy.
They were realistic. Had they resisted, most likely Thailand would have been invaded by the Imperial Japanese Army, as what had happened to French Indochina when Japan sweeped south to take out Singapore. They had the option to be neutral and not suffer military, and civilian losses; or they could have resisted ?
It was to the national interest of Thailand, at the time, to cooperate.
As for Vietnam's closed door policy, i can empathize with that. Vietnam, like China, Korea, and Japan are considered East Asian in culture, meaning there is a prevalent Confucian culture there. Like Vietnam and China, Japan had implemented a Closed Door Policy during the beginning of the Tokugawa Shogunate. Japan's doors were forced open during the Treaty of Kanagawa, where it was seen that in order to evade colonization was to modernize. During this time, the 17th - 19th centuries, was the time of European imperialism: british india, dutch malaccas, spanish philippines, and eventually french indochina. We cannot change the past @Viet , but we can learn from it. We have the benefit of hindsight.