What are some of the many diverse features of the populace in South Vietnam that prevented a strong, unified front against the Viet Cong?

There are many different religious, ethnic, and political groups in South Vietnam, including Christians (Catholics), Buddhists, Taoists, ancestral religions, various tribes, communist sympathizers, anti-Diem factions, and so forth. It proves very difficult to align all these disparate groups against the forces of Ho Chi Minh.