How Did the 1st Triumvirate Contribute to the Fall of the Roman Republic?

The First Triumvirate between Gaius Julius Caesar, Gnaius Pompeius Magnus (Pompey) and Marcus Licinius Crassus contributed to the fall of the Roman Republic by undermining the Senate, which was unable to effectively deal with an expanding and diverse empire. This was affected by the triumvirate appealing directly to popular assemblies, because their alliance conflicted directly with the conservative Optimates, who refused to change with Rome's expansion. Though ultimately because each triumvir, being an ambitious general and politician was clambering for the same place; to be top man of Rome. The very inception of the Triumvirate, and the resulting power swing it created was the beginning of the end for the Republic.
By 60BC each Pompey, Caesar and Crassus had been dismissed by the Senate. Upon Pompey's return to Italy in 62BC he sought to secure senatorial approval of his reorganisation of the eastern Mediterranean, however unliked by the optimates, under the leadership of Metellus Creticus and Cato, they stalled on this legislation and refused on granting his troops bonuses for their services. …