To say that Buddhists do not believe in a soul is an overstatement. Some prefer to say that Buddhists believe in the Latinate "consciousness," as opposed to the Anglo-Saxon "soul." As I remember, early Buddhist theologians, and no, they were not monotheists, differentiated themselves from Hindus by coining the phrase "anatman," or not self, in distinction to the Hindu "atman," or self, to emphasize its lack of "inherent" existence, or existence outside of consciousness. They did not declare that they did not believe in the existence of an atman, or a self. Buddhist frequently must differentiate themselves from "Nihilists" on such matters. This books is good starting point for detangling this semantic knot, and resolving related, central issues for oneself in the process.