Civilization does not “fall” in any classical sense. Certainly historians like to examine events and trends and draw lines in the past where one would say Rome fell, or Persia, or the Delian League; however, these are the constructs of modern eyes looking back rather than the observations of those living through those times. One does not wake up one day only to have all of society go up in flames around them.
Civilization does not fall, it withers. The fall consists of decades, maybe even centuries of decline characterized by loss of the essential character that one identifies as the community or the nation or the empire. Norms desiccate into mere husks of what they once were. The commonplace becomes scarce and the unheard of becomes commonplace. People find they cannot rely on the structure of society and little by little that structure erodes away. By the time some cataclysmic event erupts to wipe away all vestiges of ‘civilization’ it has been all but dead for some time, just awaiting the touch of the barbarian or the soothsayer to reveal it has been dead lo these many years and never knew.
Those who seek to prepare for civilization’s fall are mostly engaged in a fool’s errand, for they are unlikely to recognize the fall until it is far too late.