Rome began as a monarchy and then transitioned into a republic. After 500 years of republican government, what corrupted the republic and brought a state of anarchy?

Lust for power and fight among the political leaders.

Explanation:

During 1st Century BC political struggles were quiet often. Two triumvirates that were created strengthened this division, especially the second one. During this period the whole country was politically divided. Th period of Empire that came afterwards led to the new form of anarchy at the end of 2nd Century.