Polytheism gave birth not merely to monotheist religions, but also to dualistic ones. Dualistic religions espouse the existence of two opposing powers: good and evil.
What’s undeniable is that monotheists have a hard time dealing with the Problem of Evil.
Logically, it’s impossible. Either you believe in a single omnipotent God or you believe in two opposing powers, neither of which is omnipotent. Still, humans have a wonderful capacity to believe in contradictions.
Another key dualistic concept, particularly in Gnosticism and Manicheanism, was the sharp distinction between body and soul, between matter and spirit. Gnostics and Manicheans argued that the good god created the spirit and the soul, whereas matter and bodies are the creation of the evil god.
In fact, monotheism, as it has played out in history is a kaleidoscope of monotheist, dualistic, polytheistic and animist legacies, jumbled together under a single divine umbrella.