Following Emperor Bao Dai’s abdication, Ho Chi Minh proclaimed independence of Vietnam under the name of “Democratic Republic of Vietnam” on September 2, 1945. However, it was not recognized by any countries. In early 1946, Ho petitioned U.S. President Harry S. Truman for support for independence of Vietnam, citing the Atlantic Charter. However, the President turned down this offer since the U.S. was a close ally of France who colonized Vietnam at the time.
In order to expel the French from Vietnam, Ho Chi Minh and his government needed financial and military support. He then naturally went to the world’s second superpower, the Union of Soviet Socialist Republics (USSR) and they agreed. In fact, the USSR and China were the first two countries who recognized the legitimacy of North Vietnam in early 1950s.
Interestingly, the USSR supported Vietnam because not only were they both communists but also because they wanted to use Vietnamese people to fight against the United States, who had supported the French war effort in Vietnam since 1948. In other words, it is a proxy war.
Another fascinating question is why the U.S. was not more aggressive against North Vietnam during the conflict? They could have even used nuclear weapons, for instance, against North Vietnam but they did not. A legitimate answer would be the U.S. only wanted to stop the spread of Communism by supporting South Vietnam but did not want to be more aggressive against North Vietnam, which if happened, would have caused a regional war or even a World War III between communist countries led by the USSR and the U.S. and its capitalist allies. Indeed, the U.S. confined the war to only Vietnam with some “secret” bombings of Laos and Cambodia.