I don't really see why you should have to mention the Cold War seeing as though its not mentioned anywhere in the syllabus, but if you were going to mention the cold war then it would propbably be to do with how it influenced America's stance on communism.
Vietnam in a way did become part of the Cold War, or at least part of America's cold war policy because the American's believed it proved their theory of the 'domino effect' to be true, as Vietnamese communists had been largely influenced by their communist Chinese Neighbours - after all Ho CHi Minh had lived in China for many years as well as studying communism in Moscow in the USSR.
I think that in terms of your question the Cold War clouded America's judgement too. The American's, because of their Cold War experiences and NOrth Korean war, were unable to see the nationalistic motives behind Minh's push for communism, all they saw was a government that was trying to inforce communism on the South Vietnamese.
I think your teacher might also want to to mention the Sino-Soviet Split which was part of the Cold War and which also influenced the Vietnam War. The split basically refers to hostility between the USSR and China during the 60's, and Vietnam played a part in their tension as the two countries had different stances on the conflict in Vietnam. So North Vietnam's associations with these countries during this time would have furthur influenced the Americans, and render them unable to seperate Minh nationalist and communist views.
I hope that helps! I'm only half way through this topic and I'm finding it really confusing. lol
I'm glad I don't have to do your essay, anyways good luck!
Sarah