Julius Caesar had a very important role here. He insisted and tried forcing the rule of one man, himself, on all of the nation. With that he effectively wanted to create a Roman empire. He had great ambitions which were also the reason why he chose to do so any eventually march on Rome (he marched on Rome to threaten the government at the time). Interestingly, the actual republic fell to pieces and emperors started to properly govern only after the death of Julius Caesar.
