The Roman Empire was fundamentally a maritime empire oriented around the Mediterranean Sea. There were of course nonmaritime frontiers in the wooded north of Europe and the deserts of the Sahara and the Middle East but most, if not all, was within the watershed of the Mediterranean-Black Sea. The sea not only provided the routes for political administration and military supervision but also for trade. Sea trade was predominantly in the hands of merchants from the Levantine, the Syrians and Jews. This trade made possible regional specialization and economies of scale. Not only were goods provided cheaper as a result this trade but there was a vastly larger variety of goods available.

The Germanic tribes in the West were becoming Romanized. Germans served in the Roman Army and sometimes Germans commanded the armies of Rome. Thus the conflicts in the West were not civilization versus barbarians but instead Romanized Germans fighting against Germanized Roman armies. The battles in the East were a different matter; there it was Roman culture versus Parthian (Persian) culture. Losses in the West could be regained by diplomacy if not military operations, but losses in the East were permanent. Thus the shift of administration from Rome to Constantinople reflected this situation.

When Moslems captured the Mediterranean in the seventh century the trade routes were cut. The Vikings later also made sea trade difficult. The Magyars swept into Europe out of Central Asia and further cut trade in the east. The net result is that individual regions could not count on producing some goods for market and using the proceeds from their sale to buy the other goods which were needed. Each region had to be self-sufficient.

Self-sufficiency has its attractions but with self-sufficiency are lost the gains from specialization and the economies of scale. The levels of income and standards of living decline so there may not be any market for trade goods even if they were available. The surpluses that could support some elements of the society pursuing cultural activities disappeared and almost everyone had to grub for a living.