A typical imperial nation goes through two or three, and sometimes even four secular cycles during the course of its life. Finally, the disintegrative phase of each secular cycle will see two or three waves of political instability and civil warfare, separated by periods of fragile peace. The characteristic time scales, therefore, are a millennium for the asabiya cycle, 2 to 3 centuries for a secular cycle, and 40 to 60 years (two generations) for fathers-and-sons cycles. These are just orders of magnitude; there is no exact periodicity in any of these processes.
