Answer:
Barbarian Invasion: The many barbarian invasions were a major factor in the fall of the Classical civilizations. The Visigoths, Ostrogoths, and Vandals, together with the Huns, were Germanic tribes that raided and plundered cities, interrupted trade lines, and upended the established order. The political, economic, and social systems of the Classical civilizations are under enormous pressure as a result of these invasions.
Economic Decline: Classical civilizations experienced an economic decline. For instance, the Roman Empire's growth resulted in the depletion of resources, particularly labor, which put a burden on the economy. Additionally, these civilizations' economies were affected by inflation, currency depreciation, and falling agricultural production.
Political Unrest and Corruption: Political unrest and corruption inside the Classical civilizations itself made them more vulnerable internally.