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?

Historians have recently discovered a historical journal published in the early twentieth century. the journal contains facts based on original sources about the downfall of the early byzantium empire. historians consider this long-lost journal to be a breakthrough in their understanding of the byzantium empire. based on this information, the journal is a source.