The institutions of the Roman Republic were established as a reaction against the tyranny of Etruscan kings. Once the last of these kings, Tarquin the Proud, had been deposed, the Romans began putting in place a republican system of government that would, in theory, disperse power as much as possible, ensuring that all classes had some stake in the system.
Over the centuries, however, a number of powerful personalities arose—military men such as Pompey and Julius Caesar, who managed to arrogate substantial political power through their exploits on the field of battle. Although they were careful to keep the outward institutions of republican government in tact, in reality they subverted those institutions from within to serve their own needs. Bribery, threats, and promises of preferment were all used by many of the foremost personalities of the Roman Republic to consolidate their power among plebs and patricians alike.
However, Julius Caesar went too far. After he established himself as a Dictator, many of the political elite feared that he would go one stage further and turn himself into a king, overturning centuries of republican tradition and turning the Roman people into slaves. It was this fear that drove Brutus and his co-conspirators to assassinate Caesar on the Ides of March, 44 B.C.
The substance of Caesar's growing power had been tolerated by many, but the outward form in which it was thought that Caesar planned to express it—kingship—was completely unacceptable to the Roman political class. In the wake of Caesar's murder, many hoped that it would be possible to return to the supposedly good old days of the Republic, with power once more shared between the Senate, Consuls, and Tribunes.
But such a development was never on the cards, not least because power, though formally dispersed among the institutions of the Republic, had, in reality, always been concentrated in the hands of a privileged elite. In other words, the republican system of government was a triumph of form over substance, and once the facade of dispersed power had been broken by Caesar, there was to be no going back.