Part of the back story to my Zaneverse stories set 500 years in the future is that the 21st century turned out to be the most nightmarish century in human history. The Pan Asian Wars wipe out about half the planetary population and trash the rest of the worlds biosphere via pollution and radiation and plagues. Subsequent to that is the European Diaspora as tens of millions of indigenous Europeans flee the continent as it transforms into a third world hellhole, dominated by the Caliphate, feeding into the resurgence of Iceland and the rise of the Texas Semi Autonomous Region. All this is far in the past of the main characters, but it helped establish the world they live in just as the colonization of the New World starting five hundred years ago established *our* world.
This was all supposed to be *decades* in the future, time enough for civilized society to get set up on the Moon, Mars, asteroids, habitats, leading to *some* portion of humanity surviving The Fall at the end of the world at the beginning of the 22nd century. I fear I was too optimistic.