Rome first started as republic with fairly democratic principles for its time. its government was structured around the Senate and the Consul. For simplicity sake I will classify the senate as something similar to the legislative branch and the consulate as something like the executive branch though they don't fit these comparisons perfectly. The Senate was made up off nobles from Roman society and it was often a hereditary position with sons taking it up after there fathers they also have to be a male and a Roman citizen to become a senator. The senate made laws and edicts and also elected the consul. The consul was the most powerful position in Rome and you had to be a member of the senate to serve and not have served as the consul prior as it was a position with a term limit of 1 year and instead of 1 there were always two consuls made to check each others powers and so when one was focused on war and expanding the borders of Rome the other could stay in Rome and manage the economy. Roman society was very hierchichal and the transition to an empire was heavily influenced by the struggle between the patricans, Rome's land-holding aristocracy, who traced their ancestry to the founding of rome, and the plebians, the far more numerous citizen-commoners. The system stayed relatively the same until the reign of Julius Caesar who utilized two other men to gain influence who was Crassus and Pompey. Pompey served as co-consul with Ceasar and Crassus served as the financial backer for both there campaigns. To get to the point Ceasar was a brilliant military general and succeeded in expanding the empire greatly which allowed him to give large tracts of land to his legionaries which secured their loyalty to Ceasar personally instead of loyalty to Rome as a whole. Pompey and the senate was afraid that his buildup of influence and power would destabilize the republic so they tried to seize power from him but Ceasar returned to Rome with an army and killed those against him and established himself as Dictator for life which would signal the start of the Roman Empire.
