Answer:
Various barbarian groups weakened the empire with a series of invasions.
Explanation:
Between the 3rd and the 7th centuries AD, there was a massive migration movement of "barbarian" (non-Roman) people to the territory of the Roman Empire. These migration movements, many times took the form of military invasions in different regions of the empire and they were one for the reasons of the instability and, finally, the fall of the Roman Empire. For example, the Saxons invaded Britannia, the Lombards invaded Italy from the North, the Goths invaded the Iberian peninsula, the Vandals invaded North Africa, and the Huns invaded the Eastern region of the Empire. All these invasions weakened the empire and made it highly unstable. The barbarian invasions took place in practically all of Europe and the Mediterranean basin, marking the end of the Antiquity and the beginning of the Middle Ages.
