Is there a connection between racism and Vietnam War?

Yes. European wars had strong elements of chivalry; Asian wars showed little mercy. Example: The most vicious fighting in WW2's ETO (European Theater of Operations) was on the Russian front; between Germany and the Soviet Union (Russia). Germany, in WW2, considered Russians to be Asians (Non-Aryans) and tried to exterminate them; Russians (Soviets) replied in kind, especially when they entered Berlin in 1945.