Rome had a pretty impressive Republic, then the likes of Marius and Sulla came along - ever pushing the boundaries of unlimited power for longer and longer periods. By the time Julius Caesar arrived on the scene, there were very few traditional “Republicans” left as the “bread and circuses” crowd far outweighed the traditionalists. Even so, the transition from Julius to Imperial Rome took 17 years, and stayed that way for centuries.
Rome took a lesson from the failure of Athens. They had a deliberate balance of powers, with the Senate, consuls, tribunes, and plebs.
Caesar is usually depicted as a dictator—and therefore assumed by the folks who twist our history to be right-wing. But in fact like most dictators he was a leftist, and belonged to the Populist party.