Civil Wars:
Yes, as stated by the previous user, the barbarian tribes too the North played a large part in the downfall of Rome, but a longer-term issue can be seen in the civil wars between the Western-half of the empire (Roman Empire), and the Eastern-half of the empire (Byzantine Empire).
To give context, we must know that during the reign of Diocletian, who divided the empire into two, to allow defending easier, and gave power to another general. However, this plan backfired, as the Western half soon crumbled under pressure while the eastern half flourished. Civil Wars, civil unrest, rebellions, and many other factors also played into the effect of the fall of Rome.
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