Final answer:
Julius Caesar was a central figure in the civil war against the Roman Senate and Pompey, leading to his role as dictator of Rome. Caesar won the Battle of Pharsalus and later crossed the Rubicon, advancing his standing, but his assassination by disaffected senators ended his reign.
Step-by-step explanation:
Julius Caesar played a key role in the civil war against the Roman Senate, particularly in the conflict that pitted him against Pompey and the optimates. Caesar's series of political and military maneuvers, including his famous crossing of the Rubicon, led to a significant civil war within Rome, which is known as Caesar's Civil War. His victories, such as the Battle of Pharsalus in 48 BCE, significantly weakened the power of the Senate and Pompey, establishing him as the preeminent leader of Rome and setting the stage for his appointment as dictator. Octavian's (later Augustus) success in the subsequent civil wars owed much to the support from Caesar's veteran soldiers (Answer: c. Julius Caesar's veteran soldiers).
Sulla's march on Rome in 88 BCE was an early indicator of the imminent collapse of the Roman Republic, which foreshadowed the turbulent period that included the civil wars of the First and Second Triumvirates. By establishing the precedent of a military leader using his legions to influence Roman politics, Sulla set the stage for Caesar and others to follow his example leading to repeated civil conflicts. Caesar ultimately consolidated his power after defeating Pompey, but his efforts to control Rome as a dictator led to growing unease among some senators, culminating in his assassination in 44 BCE.