History of the East–West Schism
Disunion in the Roman Empire further contributed to disunion in the Church. The Emperor Diocletian famously 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 the Great, who established Nicene Christianity as the official religion of the Roman Empire (see Edict of Thessalonica), was the last Emperor to rule over a united Roman Empire. Following his death in 395, the division into western and eastern halves, each for a few decades still under its own Emperor, was never reunited.
The Last Legion
Orestes, who was partly of Germanic blood, was historically the "magister militum" – the senior officer of the Roman army second to the emperor. He had indeed promised his Germanic foederati a third of Italy to settle in but not to Odoacer personally. Orestes was himself a usurper, having promised the land to foederati to buy their quiescence in his rebellion against the legitimate emperor Julius Nepos. Although Orestes proclaimed his son, Romulus Augustus (derisively called "Augustulus", meaning "little Augustus") Emperor, the proclamation was not recognised as legitimate beyond the parts of the Italian Peninsula controlled by Orestes' troops. The common identification of Augustus as the "last Western Emperor" dates only from the publication of British historian Edward Gibbon's History of the Decline and Fall of the Roman Empire in the late 18th Century.