Not the entire Middle Ages but those justly called dark and what came before, from the first southward barbarian drift to the nadir of disintegration between 900 and 950 -- a stunning consolidation of obscure strands that is lit by humanistic and scholarly perspective. It has to be primarily a chronicle of battles, massacres, successions, usurpations, among people who remain only as place-names (an aspect Mr. Asimov as etymologist makes much of); it is also an education. For example, why do they seem to vanish? Because encroaching aristocracies "were without firm roots among the people. . . they could easily be defeated and replaced by another warrior caste. . . the kingdoms are simply the names we give (them) and don't represent the real population at all." The reader is frequently caught up by a significant observation: on the start of the Middle Ages (Gregory's theology); on the extremism of the Visigoths (their late conversion from Arian to Catholic Christianity); on the descent into feudalism (a response to Norse raids, later rationalized as a system). And so on to the turning point, a curious concatenation: the moldboard plow (and the horse collar), the armored knight, the rescue of ancient learning. No other juvenile compares in scope and depth, and few adult books synthesize so simply and clearly.