Trek I read a really fun article in Best of Trek #2
(published 1977) called "The Fall of the Federation", by Phillip Carpenter, which postulated the Federation splintering and imploding by the year 8000 after the galaxy had been fully explored and tensions arose about how the Federation should treat hostile species. It was written in a style similar to the Encyclopedia Galactica in Asimov's Foundation
There was mention of extra-galactic colonies, which upon learning of the Federation's fall, were forced to develop their own independent societies. They became lengend in the former Federation worlds in the Milky Way, known as the Missing Settlements.
That story really captured my imagination.