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 …

…of their own goals, as populares, bypassed traditional methods of Roman politics which were already under pressure from the failings of a system which had become outdated in governing such a continually expanding region. These conflicts with the optimates and the internal conflict within the triumvirate resulted in the failure of Rome to uphold the Republic. These factors had only one possible result. First there were three, then two and finally there was only Caesar.