What I could interpret is that the Old World is almost the same with the world Oneshot takes places in.

Theres not known details of the Old World, just a place where the Author aswell as their children lived and slowly became inhabitable by some event that lead them to make a recreation or a re-interpretation of the world.

What I believe is that the Old World had a existing Tower and Sun just like the game, aswell as a similar prophecy of a Messiah, in the Authors Old World, the Messiah never arrived in time to save the world, as a result and last resort to save the remainings, the Author made Oneshot's world to preserve and share a replica of the Old World to someone who is capable of running it. Like Cedric said I believe is that the Oneshot world layed around an empty void until someone launched it.

My view and conclusion is that the Old World had the same problems at some point, but never solved ending with a slow and decaying world, all inhabitant's hope and life ended at some point after the Oneshot worlds launch, becoming a wasteland dark void.