A common fact about Rome is its multiple phases. So it’s very important to remember that Rome itself 

Indeed, its origins both as a historical and cultural study are very interesting, but what remains as a factual reality is how the Roman entity did not come about in its size and duration as just an empire, but went through a lot of phases.

Prior to the advent of the Pax Romana, a period in which Rome reached its peak both in cultural, geographic, and military outcomes, Rome was known as a Republic. It functioned peer a body of representatives who deemed it necessary for Rome to not be held in the grip of one human. 

This Republic, created in 509 BC, was toppled when Emperor Augustus (known as Octavian back then) won the civil war which was instigated after the assasination of Julius Caesar. He led the Roman Republic into the Imperial period, often being cited for it being the part of Rome where prosperity flourished.

How did Rome become a Republic?

In those eras, it was uncommon to find a system of governance which were not centered around a monarch. This style of governance was not unknown to the early state. 

From the moment it came into existence, until the foundation of the Republic, Rome was a monarchy. Its expansion and growth led the locals of the state to wonder at a system that sought further privilege and authority for them, and not just one person. 

The Civil War

In the period proceeding with the assasination of Julius Caesar, Pompei’s campaigns, and Augustus’s placement on the throne, Rome was tarnished into a civil war consisting of sides that supported military generals who each vied for control. 

Towards the end of the civil wars, Augustus came out victorious, starting an era of growth, stability, and geographic control which, for that time, controlled much of the known world around the Mediterranean Sea. 

Outcome

This entity existed up until the first hundred years AD, when Germanic tribes began to come from the north, causing the demise of the Western half of the Roman Empire.