If you look at the history of Western Europe after the collapse of the Roman Empire you'll find that Society largely collapsed into small towns each governed by their own local Lord or perhaps a king but constantly subject to attack from all sides by neighboring powers in distant foreign powers who would occasionally sweep through and murder every one except for the desirable women and children. Occasionally a man's life might be spared if agreed to be a slave or serf for another Lord or King. The situation was exacerbated by the effects of the Justinian plague and the onset of volcanic winter in the year 536.