If you step far enough back to look at the whole of human history, you will begin to see a very plain rhythm: a heartbeat of civilization. Steep climbs out of disease and ignorance into the light of medicine and learning — and then a sudden collapse back into darkness. And it is in that darkness that most humans have lived their lives: poor, nasty, brutish, and short.
The pattern is always the same: at the height of a civilization’s powers something catastrophic seems to occur — a loss of will, a failure of nerve, and above all an unwillingness to identify with the values and customs that have produced such wonders.
When all is said and done, Civilizations do not fall because of the barbarians at the gates. Nor does a great city fall from the death wish of bored and morally bankrupt stewards presumably sworn to its defense. Civilizations fall only because each citizen of the city comes to accept that nothing can be done to rally and rebuild broken walls; that ground lost may never be recovered; and that greatness lived in our grandparents but not our grandchildren. Yes, our betters tell us these things daily. But that doesn’t mean we have to believe it.
As always, go read all of The Undefended City.