The Fall of Chronopolis

There is real time... and there is potential time. By controlling the difference, the Chronotic Empire came into existence and maintained itself over a thousand years of human history. Its Time Fleets, armadas of time-travelling fortresses, patrolled its temporal borders relentlessly, blotting out potential-time deviations, erasing errors of history that might undermine the empire. But nevertheless the empire's days were numbered, for somewhere in its own future was the century of the Hegemony, its implacable enemy.