It’s actually a cool belief system from what I’ve read, known as Tengriism; they had their own beliefs but (and I hope I have this right) that whatever religious worldview prevailed locally was considered not just valid as a personal or cultural expression, but actually metaphysically true as well. That seems fantastic, doesn’t it? Patchwork metaphysics.
I’m not an expert but from what I’ve read most ancient world deities were attached to certain geographies (it would be reasonable to sort of leave the boundaries of your gods) so I wonder if this comes from that tradition. The roman catholics sure successfully weaponized monotheism.
That’s one way. Another was syncretism. The Romans famously stole the Greek gods, but they also worshipped isis for example. “That god resonates with me, so sure why not”.
I just love how fun it would be to believe that yes, god is the Creator of the Cosmos and he lives in the sky, I have a rich cosmogony that tries to explain the Universe and Everything…But also, if you cross that mountain to the west and traverse the river beyond, them you’ll be in another part of our empire where the universe was created by the boogers of a Titan or something like that I was too busy picking up my arrows to listen. Bless them.