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
With the end of the last Republican civil war, the Republic was replaced by the Empire. The reign of Augustus would usher in the golden era of Roman culture and produce a stability which Rome had not seen in over a century. With Rome in control of the entire Mediterranean world, a peace would reign in the Roman world for centuries after the death of Augustus: the so-called Pax Romana (Roman Peace).