Which sentence describes a cause of the decline of the Roman republic

There was no single cause or event which led to the downfall of the Roman Republic; social and political instability, rapid expansion, and corruption among the rich and powerful all played a role. Historians traditionally consider that the Republic began in 509 B. C. with the overthrow of the Roman Kingdom and that it ended in 27 B. C. with the establishment of the Roman Empire at the hands of Augustus