Full Idea
The first monotheist religion known to us appeared in Egypt c.1350 BCE, when Pharaoh Akenaten declared that one of minor deities of the Egyptian pantheon, the god Aten, was in fact the supreme power ruling the universe.
Gist of Idea
Monotheism appeared in Egypt in 1350 BCE, when the god Aten was declared supreme
Source
Yuval Noah Harari (Sapiens: brief history of humankind [2014], 12 'God')
Book Reference
Harari,Yuval Noah: 'Sapiens: a brief history of Humankind' [Vintage 2014], p.242
A Reaction
Zeus seems to have started like a tribal chief, and eventually turned into something like God.