What historical factors contributed to the demise of the Roman Republic?

The Roman Republic ended sometime between 49 BC and 27 BC; the first date being when Caesar crossed the Rubicon, which started the terminal civil wars of the Republic, and the second being Augustus’ formal “coronation” as princeps, and the first de facto emperor. The “demise of the Roman Republic” should be understood, in my opinion, as a political transformation, from a collaborative oligarchy to a monarchy. The factors that caused this demise must therefore have played a destabilizing role in the political culture in the Republic, that allowed that transformation to happen. These include the rise of “client armies”, after Marius’ reforms; the influx of new political ideas in the culturing melting pot that was the heart of a large empire; and the enormous new opportunities for wealth and power that exacerbated elite rivalry.