Romulus Augustulus
Flavius Romulus Augustus (c. AD 460 – after AD 476; possibly still alive as late as AD 507), known derisively and historiographically as Romulus Augustulus, was the Roman emperor who ruled the Western Roman Empire from 31 October 475 until 4 September 476. He is often described as the "last Western Roman emperor", though some historians consider this to be Julius Nepos. His deposition by Odoacer traditionally marks the end of the Roman Empire in the West, the end of Ancient Rome, and the beginning of the Middle Ages in Western Europe.
Christianity in the 4th century
Disunion in the Roman Empire further contributed to disunion in the Church. Emperor Diocletian divided the administration of the eastern and western portions of the empire in the early 4th century, though subsequent leaders (including Constantine) aspired to and sometimes gained control of both regions. Theodosius I, who established Christianity as the official religion of the Roman Empire, died in 395 and was the last emperor to rule over a united Roman Empire; following his death, the division into western and eastern halves, each under its own emperor, became permanent. By the end of the 5th century, the Western Roman Empire had been overrun by the Germanic tribes, while the Eastern Roman Empire (known also as the Byzantine Empire) continued to thrive. Thus, the political unity of the Roman Empire was the first to fall.