Final answer:
The closest concept of God that the Zulu demonstrated was polytheism, a belief system that incorporates multiple deities, which was adapted into Africanized forms of Christianity and Islam.
Step-by-step explanation:
Many missionaries eventually confirmed that the closest the Zulu demonstrated to having any kind of understanding of God was essentially a rudimentary form of polytheism. This is indicative of a religion based on belief in multiple deities as opposed to a monotheistic faith, which believes in a single deity. Anthropologists note that the traditional practices and rituals of African peoples often adapted well to Christianity and Islam because these religions were open to incorporating some aspects of existing African belief systems, leading to a unique Africanization of the faiths.