The classic example of this on a massive scale is, of course, medieval Europe. All Roman-imposed centralized order broke down in a slow apocalypse and control r

The classic example of this on a massive scale is, of course, medieval Europe. All Roman-imposed centralized order broke down in a slow apocalypse and control reverted to local armed gangs... which then formed alliances and feudal pecking orders and gradually recentralized into kingdoms and empires.