Again, from The TOF Spot blog:
The World of Late Antiquity was in serious decline. Global warming, with its longer growing seasons and more expansive agriculture, had ended and global cooling had set in. The bubonic plague had, well, plagued the Empire. Population had dropped 20% and cultivated land had contracted, esp. in North Africa, Rome’s breadbasket after the wheat of Egypt had been diverted to Constantinople by the New World Order. Town life in Western Europe had virtually ceased even before the Germans crossed the frozen Rhine on the last day of AD 406.
The Empire itself was being called Romania by folks sensing that they were now all in the same lifeboat together. The Gauls had finally given up Gallic for Latin, and the Iberians likewise, though both spoke it with funny accents. Case endings were no longer being pronounced, though they were still being meticulously spelled. (Though odd spelling mistakes are creeping in as the new semi-literate elites have begun spelling things they way they sound.) The Latin demonstrative ille has been clipped to become il or le or even el in different dialects and the definite article has appeared as if by magic.
The Empire is a large agribusiness with luxury goods coming in from the east and bulk commodities circulating on the Mediterranean, the backbone and center of the classical world. Anyone much more than a day’s cart ride from the sea coast is S.O.L. bulk shipment-wise, save for what can be raised locally. The grain grown in Egypt and Africa is destined for the welfare lines in the great cities. The peasants in the provinces live in poverty and oppression, and many have been placing themselves under the protection of local counts or (in the West) barbarian barons. (Outside the Empire, in Ireland, it is different: the farms are smaller, the peasants are independent, and they are well-armed.)
Read the rest at his blog; much more readable, with rather more information, than my high school history book.