Who led the nationalist movement in Vietnam after World War II?

The nationalist movement was led by Emperor Bao Dai.

Explanation:

The Vietnam War occurred during the Cold War period. As several other wars i this period this one was also based on the fight between communist and capitalist movements. Vietnam became internally divided because it had two major fractions, one being the communist one in the north, and one being the nationalist one in the south.

The communist fraction was the Viet Minh, and it was supported by the communist countries. The nationalist fraction, led by Emperor Bao Dai was supported by the anti-communist countries. The war didn't just occurred on the territory of Vietnam, but it also was on the territories of Laos and Cambodia. The end result was a win for the communist fractions and all three countries became communist.