Final answer:
With the death of Marc Antony, Octavian became the uncontested ruler of Rome and subsequently founded the Roman Empire, thus marking the end of the Roman Republic and the beginning of a new era under his reign as Emperor Augustus.
Step-by-step explanation:
After the death of Marc Antony, Octavian, who was by then the sole power in Rome, faced little opposition and took significant steps to consolidate his authority and transform the Roman Republic into the Roman Empire.
In doing so, Octavian, who would assume the title Augustus, laid the foundation for a political structure that would last for centuries. He installed a system called the principate, which maintained the facade of the Republic but was essentially a form of autocratic rule, and thereby became the first Roman Emperor.
This shift from Republic to Empire represented the ushering in of a new era in Roman history, moving away from the turbulence of civil wars and political strife that had characterized the preceding years.