When did man create the concept of a monotheistic god?

I know that man wrote his bible somewhere around 1500 B.C. and before that civilizations where mostly all polytheistic like the ancient Greeks, Romans, Egypt, and many Asian cultures. So around what years do you suppose that polytheism started to became obsolete and monotheism started taking over? What made humans change their views to just one all powerful god instead of multiple ones with their own specialty?