here that a fictitious historical text book could be written about Poul Anderson's History of Technic Civilization. It seems that Poul Anderson did write it:
"I wrote out the entire historical scheme explicitly, with a time chart, star maps, and related aids."
-Poul Anderson, "Concerning Future Histories" IN SFWA Bulletin, Fall 1979, p. 10.
Would we like to read this scheme? Or should it be regarded as part of the background material and therefore not as part of the finished work?
Anderson wrote in the same article:
"...it seems obvious - and certainly there is a good bit of detail in my head, even though I'll never put it into print - that humanity in this imaginary universe did muddle through its present set of crises; that a more humane order of things did evolve; that English, eventually shifting enough to be called 'Anglic,' became the main international language, without suppressing the rest..." (p. 11)
(Later, David Falkayn in space is surprised to be addressed not in League Latin but in German.)
Anderson's thoughts on the Chaos cannot be published because they were only in his head. A work set in this period could be near future or even contemporary fiction without any explicit reference connecting it to the later Technic History. The only such reference in "The Saturn Game," set in the mid-twenty first century, is that one character was brought up in the Jerusalem Catholic Church. So that religious change or split had occurred that early. What happened to Rome during the Chaos? (In James Blish's Black Easter/The Day After Judgment, Rome was nuked and the Cardinals met in Venice to elect a new Pope but that is in a different timeline.)