I see the "barbarian invasions" as being the result if poorly handled migrations of Germanic peoples into the Roman empire in the late 300s and early 400s. Most famously, the Gothic War, which was the result of a poor treatment of Goths seeking to emigrate into Roman lands, seeking to escape from Hunnic pressur north of the Danube. The poor treatment of these refugees by the Romans, led to them revolting and the infamous battle of Adrianople. The Gothic War was a very real conflict for the Romans, but its origins come from the Goth's seeking a home within the Roman Empire. The Vandal kingdom of North Africa, was also the result of a migration of Vandals, sanctioned by the Western Empire into Spain. The Vandals then moved into North Africa and established an independent kingdom there. Once again, the greatest enemies of Rome were those that had been intentionally let into her borders. The Barbarian Invasions of Rome were, in my eyes, failed migrations that were handled poorly by the Roman government, who treated the refugees poorly, triggering them into action. Another major cause is that Romans began giving more and more power and autonomy to the barbarians, particularly the Goths, whom the romans allowed to live separately and independently of the rest of the empire. Before, barbarians had been split up, and integrated into the larger roman society, now they lived as independent kingdoms within Roman borders, with their own militaries which they would turn on Rome, such as in the case of Alaric and the Goths, and Genseric and the Vandals.