History of the Roman Empire disputes about the supreme authority, this finally formalised a peaceful succession of the emperor: in each half a "Caesar" would rise up to replace the "Augustus" and select a new "Caesar". On May 1, 305, Diocletian and Maximian abdicated in favour of their "Caesars". Galerius named the two new "Caesars": his nephew Maximinus for himself, and Flavius Valerius Severus for Constantius. The arrangement worked well under Diocletian and Maximian and shortly thereafter. The internal tensions within the Roman government were less acute than they had been. In "The Decline and Fall of the Roman Empire", Edward Gibbon notes that this
Historiography of the fall of the Western Roman Empire the Huns as deeply significant in the fall of the Western Empire long before they themselves became a military threat to the Empire. He postulates that the Hunnic expansion caused unprecedented immigration in 376 and 406 by barbarian groupings who had become significantly more politically and militarily capable than in previous eras. This impacted an empire already at maximum stretch due to the Sassanid pressure. Essentially he argues that the external pressures of 376–470 could have brought the Western Empire down at any point in its history. He disputes Gibbon's contention that Christianity and moral decay led to the decline.