Final answer:
The nomadic Arabs were predominantly polytheistic, worshipping a multitude of deities before the emergence of Islam with the Prophet Muhammad, which marked a return to monotheistic beliefs.
Step-by-step explanation:
Before the birth of the Prophet Muhammad, the nomadic Arabs were predominantly polytheistic. They worshipped numerous deities and practiced idolatry, which was a common form of religious belief in the Arabian Peninsula at the time. This period is known in Islamic history as jahiliyyah, often translated as 'The Age of Ignorance,' which was a time before the spread of monotheism through the Prophet Muhammad's teachings.
In the context of early Islamic belief, it was thought that the descendants of Ishmael gradually drifted away from their original monotheistic beliefs and started to practice idolatry. The advent of Islam, through Prophet Muhammad, was seen as a return to the monotheistic worship of Allah, and a departure from the polytheism that was pervasive among the Arabs.