The Cause of the Collapse of Civilizations

Civilizations fall rapidly due to an inescapable catastrophe. Water sources dry up. A powerful empire invades.

Civilizations fall slowly due to a moral catastrophe. A moral catastrophe is not a failure of arms or food. It's a failure of the sustaining virtues of the civilization. As the society tumbles slowly downward, it will encounter defeat in battle, collapse of its infrastructure and food shortages. But these are symptoms, not causes. The cause is the degeneration of the society and its people.

Daniel Greenfield, Virtue and the Moral Fall of Civilization