How might imperialism be one of the causes of the vietnam war?

The Vietnamese wanted to expand so America couldn't just let it happen even though everyone else let and aided the both sides of American's wars. Like for ex: If America or the Vietnamese didn't want to go to war. Than they wouldn't be imposing there government and rules any where else. Thus no imperialism if there was now war. Which means that the Vietnam War was manly dealing with imperialism from the Vietnamese. Imposing there rule on other parts of Asia.