Final answer:
The fall of the Roman Republic was primarily caused by conflict between the aristocracy and ordinary citizens, along with economic failures and social unrest.
Step-by-step explanation:
The primary cause of the fall of the Roman Republic was the conflict between the aristocracy and ordinary citizens. This conflict led to political instability and social unrest. Other factors that contributed to the fall were economic failures, the influx of slaves causing an unemployment crisis, and the rise of populist ideas.
Modern republics such as the United States are less likely to collapse for the same reasons. The United States, for example, has a system of checks and balances and a strong democratic tradition that helps to prevent the concentration of power in a single group.