This chapter considers Rome’s rise from a small kingdom on the Tiber River in Central Italy to dominating the entire Mediterranean and becoming one of the most powerful geopolitical forces in world history. Following scholars as diverse as Polybius, Machiavelli, and Montesquieu, it argues that the institutions of the Roman Republic were the key to its success. After its transition to republican governance in 509 BC, Rome succeeded in defeating neighboring tribes to control the entire Italian Peninsula and setting it up for rivalry with the other great republican powerhouse of the western Mediterranean: Carthage. Rome destroyed Carthage in a series of three Punic Wars. Finally, it dispensed with several autocratic kingdoms of the Hellenic world in the eastern Mediterranean, including Macedon. In just a few short centuries, Rome found itself transformed from a small city-state into a global superpower standing astride the entire civilized world.