Saylor.org's Ancient Civilizations of the World/The Roman Empire
Rome did not become an empire that controlled the entire peripheral lands of the Mediterranean Sea over night. Indeed, much of Rome's imperial expansion occurred before the official creation of the Empire. Historical debate continues over whether the Roman Republic had actively sought an empire through conquest or if numerous acts of defense from outside aggression and victory over aggressors inevitably pulled Rome into acquiring more land.
Less debatable are the events that lead to civil war which precipitated victory for Octavian who would become Augustus Caesar, the first Roman Emperor.