Octavian's rise to power signaled an end to the roman republic

After the assassination of Julius Caeser, Octavian together with Mark Anthony and Lepidus formed the Second Triumvirate.  Their army won against the republican army at the Battle of Philippi, Macedonia in 42 B.C.  After the battle they divided the territories of Rome amongst themselves.  Later Anthony fell in love with the Egyptian queen Cleopatra and gave her some of Rome’s territories in the east.  He also divorced Octavian’s sister and war erupted between the two.  Octavian defeated the combined naval fleet of Anthony and Cleopatra at the Battle of Actium on September 2, 31 B.C.  Both of them committed suicide and Egypt fell under Roman rule.  This marked the end of the Roman Republic and the beginning of the Roman Empire.