3 – The Split Empire
When Diocletian became emperor in 284 AD, he realized that it was no longer possible for one man to rule the vast empire. He made Maximian his co-emperor sometime in 285 AD with Empire split into east and west; Nicomedia was the original capital although it was changed to Constantinople in 330 AD. From this point onwards, the Senate would be ignored. In the past, it had advised the emperor on matters of state. The power of the empire was supposed to be based on an active military which became a problem when the empire’s military strength waned.
Some of the later emperors never even set foot in Rome and while the division offered an initial boost in strength, it ultimately made the Western Empire more vulnerable to attack. Rome had been having issues with Germanic tribes for centuries but was usually able to repel them or buy them off with land, an invitation to join the army or citizenship. The split became permanent in 330 AD.
Both halves of the empire prospered equally until the defeat of Eastern Emperor Valens at Adrianople in 378 AD. East and West effectively broke apart due to internal and external problems during the reign of Theodosius I. During his spell as emperor (379-395 AD), the empire’s resources and boundaries became overstretched, and he spent much of his time spreading Christianity and stamping out pagan practices. The Gothic War was mainly fought by Eastern Empire forces, but it weakened the Empire in the West.
Theodosius was the last person to rule over a unified empire. Upon his death, the Western and Eastern parts were governed by separate emperors. During the 5th Century AD, certain rulers actually moved the seat of the Western Empire away from Rome with Ravenna and Milan serving as capital at different stages. The split worked well for the East which lasted another 1,000 years but the West completely crumbled.