Why Empires Fall by Peter Heather

Argues that the fall of the Western Roman Empire was driven primarily by external military pressures and migrations that overwhelmed frontier defenses, combined with political fragmentation, recruitment failures, and fiscal strain within the empire. Tracing events from the Hunnic push of peoples across the borders through the Gothic settlements, sackings of Rome, and the collapse of imperial authority in the fifth century, it emphasizes contingency and military causation rather than inevitable internal decadence or solely economic or environmental explanations. The book contends that a series of military defeats, shifting loyalties, and the erosion of centralized coercive power turned frontier problems into systemic collapse.

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