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.
OTOH, Kings probably shouldn't be considered an alternate history, since it's really just a retelling of a biblical tale, but in the same light, it's paradoxical that the story of David and Goliath could still be a part of their bible and yet be played out in exact details thousands of years later, with no one the wiser, especially since they've made it clear that religion is an integral part of the society; it's a chicken-and-egg tale.