Politically, the rise of Julius Caesar hastened the end of the Roman Republic and its subsequent replacement by an imperial system of government.
Caesar was assassinated by members of the Roman political elite precisely because they thought that he represented a threat to the republic and that he was going to make himself king. To ardent republicans like Brutus, this was unthinkable, and so he, along with other conspirators, murdered Caesar on the Ides of March, 44 BCE.
Though not one of Caesar's assassins, Cicero was certainly one of his most implacable opponents. As with much of the Roman political establishment, he was genuinely worried that Caesar would destroy the republic with all its old venerable traditions, make himself king, and effectively turn the Roman people into slaves.
Cicero understood all too well that rule by one man, no matter how wise, can all too quickly turn into outright tyranny. That was his concern with Augustus no less than with Caesar, and it was Cicero's bold expression of this concern that would ultimately cost him his life.
One of the great ironies of Roman history is that the Roman Empire concentrated even greater power in the hands of the emperor than Caesar enjoyed. Although Caesar's grand-nephew Augustus, the first Roman emperor, was not a king, he and his successors certainly enjoyed as great, if not greater, power than any king of that time. Unwittingly, then, Caesar's assassins ushered in a political system that would become more despotic than anything envisaged by the dictator.
With the end of the republic went a political system that had lasted for centuries, a relatively democratic system in which power had been shared. During the Roman Empire, however, ultimate power was vested in one individual, the emperor.
Although Augustus cleverly gave the impression that he was ruling according to the old republican traditions, in actual fact he wielded far greater power than any of the old Roman kings ever had.
Later emperors, such as the notorious Caligula, weren't as clever as Augustus and made no secret of the fact that they were all-powerful despots who could do pretty much as they pleased. Caligula, and many other emperors like him, proved Cicero—who had warned of the dangers of one-man rule—absolutely right.