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 Fall of the Roman Empire (film)
The film's plot is only loosely based on actual historical events. However, in the long-established view of Roman history, Marcus Aurelius is considered as the last of the Five Good Emperors whose time is considered the best of Roman imperial history. Commodus is generally considered to have fallen far below the standard set by his father and the four earlier Emperors, and his reign is considered as the beginning of the decline - though that would still take several centuries.