Full Idea
Polytheism gave birth to monotheism, and to dualistic religions. Dualism explains that the entire universe is a battleground between good and evil forces, and everything that happens is part of that struggle.
Gist of Idea
Dualist religions see everything as a battleground of good and evil forces
Source
Yuval Noah Harari (Sapiens: brief history of humankind [2014], 12 'Battle')
Book Reference
Harari,Yuval Noah: 'Sapiens: a brief history of Humankind' [Vintage 2014], p.245
A Reaction
Presumably we are supposed to support the good guys, so the gods are not equals. God v Satan seems the right model, but Satan has to be beyond God's control, or else the problem of evil has to be solved. Empedocles held something like this.
Related Idea
Idea 552 Empedocles said good and evil were the basic principles [Empedocles, by Aristotle]