How come Italy used to be the center of the civilized world,

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those barbarian tribes later developed into the feudal kingdoms of europe and far less directly the "enlightened monarchies" of 1400+, sure, but i dont get what your point is, that has nothing to do with the state of rome in the middle of the 5th century

The nation of England did not have its Feudal roots established by barbarians; most historians agree that the Romans played a much larger role in England's development than Barbarians did.