Which led most directly to the Roman Republic's demise and its transition to an empire?

A) consults staying in power too long

B) slave revolts

C) war with the Etruscans

D) the failure of direct democracy

B - Slave revolts.

The revolt of Spartacus, which was also the most famous slave uprising in the history of the Roman Empire, lead to questions about the usefulness and effectiveness of the current governmental system in Rome. This, along with other factors, made them plunge into a crisis which ended through the transition to an empire.