In Collapse of a “Hyperpower”, Victor Davis Hanson reviews The Fall of Rome and the End of Civilization, by Bryan Ward-Perkins, and cites this passage:
The end of the Roman West witnessed horrors and dislocation of a kind I sincerely hope never to have to live through; and it destroyed a complex civilization, throwing the inhabitants of the West back to a standard of living typical of prehistorical times. Romans before the fall were as certain as we are today that their world would continue forever substantially unchanged. They were wrong. We should be wise not to repeat their complacency.