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.
Final War of the Roman Republic
Following the end of the war, Octavian brought peace to the Roman state that had been plagued by a century of civil wars. Octavian became the most powerful man in the Roman world and the Senate bestowed upon him the name of Augustus in 27 BC. Octavian, now Augustus, would be the first Roman Emperor and would transform the oligarchic/democratic Republic into the autocratic Roman Empire.