The most accurate statement that summarizes the figures and events that led to the fall of the Roman Republic is:
The Roman Republic fell due to the first civil war and political struggles between the Populares and Optimates.
This response effectively captures the critical political conflict during the time, which was largely characterized by the struggle for power between the Populares (who sought to represent the interests of the common people) and the Optimates (who represented the aristocratic elite) leading up to and during the first civil war between Julius Caesar and Pompey.