Greek religion didn't come from nothing either: proto-Greek society was simply following certain gods that they considered important for them (fish-god/soil-god

Greek religion didn't come from nothing either: proto-Greek society was simply following certain gods that they considered important for them (fish-god/soil-god), and then when one area managed to invade another area they reconciled their religious allegiance by assuming the god of the invader was simply "stronger" than the other one.