Communism and Buddhism in Vietnam had not been much of a concern until the middle of this century. When Ho Chi Minh began to gain popular support during the 1940's and 1950's, the Buddhists as a whole did not share common interests. It was not until the conflict between the French and Americans escalated that the Buddhists began to make connections with the communist forces.
There is very little, if any, place for organized religion in communist ideology. Yet the Buddhist protests against Diem and American involvement in Vietnam was one of the most powerful images of the war. Buddhism began to equate to nationalism, and this notion would be the one that linked communism and religion.
The Buddhists realized, that under American control they would loose many of their freedoms. Since Diem, and his American supporters, were primary Catholic (or at least Christian) the Buddhists began to understand the ramifications of becoming a religious minority. They would loose freedom, political power and in many ways a heritage that spanned thousands of years. It is out of this frustration that the Buddhists became nationalists, and protested American involvement. There is little evidence to suggest that the Buddhists were communist sympathizers, but they preferred national interests to international control.