What does the Roman Republic gain and what does it lose as it acquires an empire?
The process of becoming an Empire was thrust unwillingly on the Roman Republic. During the Second Punic War, soldiers and commanders who were defeated by Hannibal were exiled to Sicily. As a result, when Scipio Africanus led the forces which ultimately defeated Hannibal, soldier's loyalties were no longer to the Republic, but to the individual military commander. This enabled Julius Caesar to march on Rome and declare himself Dictator, as was provided by the Roman Constitution. By becoming an Empire, Rome was able to extend it's empire to make the entire Mediterranean a Roman Lake, in fact they called it "Mare Nostrum" (Our Sea). The price they paid for empire was rule by one person. It his highly unlikely that Rome would have suffered under a Caligula or Nero had the Republic remained in place. Additionally, the instability that marked the later Emperors would have been avoided. It is possible that Rome would have lasted longer than it did, in fact.