Why are fans so concerned about backstory and wondering if the world in Kings is a divergence from ours. I seem to remember a little movie called Star Wars which began its story in the middle!
Because Star Wars wasn't an alternate history. That's the point of alternate histories: to explore the consequences of a divergence in the established history.
Ok, everyone repeat after me: "Kings is not alternative history!"
Got that? Kings is a modern day retelling of the story of David. That's it. Whatever could be brought right from the Bible to the modern world was, whatever needed to be updated was. Hence Goliath is a tank, Samuel is a Reverend instead of a prophet. Real classical music was used so the viewer could identify it, but it doesn't matter what country the composer lived in, or even when he composed it. Whatever is not relevant to the story of David is not included. Just sit back and enjoy the characters/ride. There will never be an explanation for the world, or an examination of the branching point because it doesn't exist.