page_title: Fall of the Western Roman Empire
section_title: Reunification and political division
hierarchical_section_title: Fall of the Western Roman Empire / Height of power, crises, and recoveries / Reunification and political division
caption_attribution_description: English: historic map of Roman Empire during the first tetrarchy
context_page_description: The fall of the Western Roman Empire was the process of decline in the Western Roman Empire in which the Empire failed to enforce its rule, and its vast territory was divided into several successor polities. The Roman Empire lost the strengths that had allowed it to exercise effective control over its Western provinces; modern historians posit factors including the effectiveness and numbers of the army, the health and numbers of the Roman population, the strength of the economy, the competence of the Emperors, the internal struggles for power, the religious changes of the period, and the efficiency of the civil administration. Increasing pressure from invading barbarians outside Roman culture also contributed greatly to the collapse. The reasons for the collapse are major subjects of the historiography of the ancient world and they inform much modern discourse on state failure.
  In 376, unmanageable numbers of Goths and other non-Roman people, fleeing from the Huns, entered the Empire.
context_section_description: Aurelian reunited the empire in 274, and from 284 Diocletian and his successors reorganized it with more emphasis on the military. John the Lydian, writing over two centuries later, reported that Diocletian's army at one point totaled 389,704 men, plus 45,562 in the fleets, and numbers may have increased later. With the limited communications of the time, both the European and the Eastern frontiers needed the attention of their own supreme commanders. Diocletian tried to solve this problem by re-establishing an adoptive succession with a senior (Augustus) and junior (Caesar) emperor in each half of the Empire, but this system of tetrarchy broke down within one generation; the hereditary principle re-established itself with generally unfortunate results, and thereafter civil war became again the main method of establishing new imperial regimes. Although Constantine the Great (in office 306 to 337) again re-united the Empire, towards the end of the fourth century the need for division was generally accepted. From then on, the Empire existed in constant tension between the need for two emperors and their mutual mistrust.
  Until late in the fourth century the united Empire retained sufficient power to launch attacks against its enemies in Germania and in the Sassanid Empire. Receptio of barbarians became widely practised: imperial authorities admitted potentially hostile groups into the Empire, split them up, and allotted to them lands, status, and duties within the imperial system.
  In this way many groups provided unfree workers (coloni) for Roman landowners, and recruits (laeti) for the Roman army. Sometimes their leaders became officers. Normally the Romans managed the process carefully, with sufficient military force on hand to ensure compliance, and cultural assimilation followed over the next generation or two.
caption: The Roman Empire under the Tetrarchy, showing the dioceses and the four Tetrarchs' zones of responsibility
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