Must be in Middle Ages.
Monotheism is the belief that there is only one God. Perhaps the oldest monotheistic religion is Judaism. The original Israelites were polytheistic in a sense, since they did not deny the existence of other gods in addition to their own. However, after being exiled to Babylonia in 586 BC, the Judeans turned to a truly monotheistic religion, where the God of Israel was seen as the universal God ruling the destiny of all nations. The scriptures of Judaism became part of the teachings of the two most widespread monotheistic religions, Christianity and Islam. More developed than earlier polytheistic beliefs, monotheistic religions tend to encompass and structure the entire lifestyles of the people who practice them.