Vietnam was occupied by Japan from '40 until '45. Of interest, is the Royal Navy Battleship HMS Prince of Wales (of fighting the German Bismarck battleship fame) and battlecruiser HMS Repulse were both sunk by land based Japanese bombers, which took off from airfields in Vietnam. For the first time in naval history, a battleship which was underway, and fighting back, was sunk by airpower alone (10 December 1941).
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Vietnam was called Vietnam after World War 2.
Vietnam became independent from France after World War II, when the Japanese War in the Pacific triggered the invasion of French Indochina in 1941. Source: http://en.wikipedia.org/wiki/Vietnam#History
America's last declaration of war was on 11 December 1941.
In order of major impact; the Vietnamese people, the US, Australians, and the world involved with the cold war in general.
Until the Vietnam War, few people ever heard of Vietnam. Therefore, Vietnam's sense of National Identity was STRONG.
The Vietnam war from 1959 to 1975.
There was no such person. Vietnam was then French Indochina, a colony of France, and after the summer of 1941 it was occupied by the Japanese.
Since US citizens were drafted to fight the war; it had a negative impact.
A reluctance to enter future conflicts
Well, a lot of them died.
With protests and riots.