First there was the Roman Kingdom, then the Roman Republic and then the Roman Empire. But what was it that made it an empire the third time, rather than just going back to being a kingdom again?
Lucius Tarquinius Superbus was the last rex Romae (=king of Rome), Julius Caesar held the office of dictator perpetuo (=dictator for life) while Augustus was the first imperator (=emperor).
But isn't an emperor a king that is king over other—less powerful—kings? If so, who were these kings and kingdoms under Emperor Augustus?
Did the Romans themselves consider themselves as part of an empire rather than a kingdom? Or is this more of a modern distinction by historians, just to keep the time periods apart?