Europe and the Faith by Hilaire Belloc — Read

So far we have traced the fortunes of the Roman Empire (that is of European civilization and of the Catholic Church with which that civilization was identified) from the origins both of the Church and of the Empire, to the turning point of the fifth century. We have seen the character of that turning point.

There was a gradual decline in the power of the central monarchy, an increasing use of auxiliary barbarian troops in the army upon which Roman society was founded, until at last (in the years from 400 to 500 A. D.) authority, though Roman in every detail of its form, gradually ceased to be exercised from Rome or Constantinople, but fell imperceptibly into the hands of a number of local governments. We have seen that the administration of these local governments usually devolved on the chief officers of the auxiliary barbarian troops, who were also, as a rule, their chieftains by some kind of inheritance.