The Germanic invasions destroyed neither the Mediterranean unity of the ancient world, nor what may be regarded as the truly essential features of the Roman culture as it still existed in the 5th century, at a time when there was no longer an Emperor in the West.

He also became prominent in the nonviolent resistance to the Germans who occupied Belgium in World War I. Pirenne argued that profound social economic cultural and religious movements in the long-term resulted from equally profound underlying causes and this attitude influenced Marc Bloch and the outlook of the French Annales School of social history.