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.
List of Roman consuls
As an institution, the consulship survived the abdication of the last emperor of the West, and for a time consuls continued to be appointed, one representing the Eastern Roman Empire, and the other the Western, even as the Western Empire dissolved as a political entity. The last consuls appointed represented only the Eastern Empire, until finally the title became the sole province of the Emperor, who might or might not assume it upon taking office.