Excerpts from Books and Wikipedia
"After the Roman Senate declared war on the Egyptian queen Cleopatra, Antony, her lover and ally, betrayed the Roman government and joined the war on Cleopatra's side. After the decisive victory for Octavian at the Battle of Actium, Cleopatra and Antony withdrew to Alexandria, where Octavian besieged the city until both Antony and Cleopatra committed suicide.
Following the end of the war, Octavian brought peace to the Roman state that had been plagued by a century of civil wars. Octavian became the most powerful man in the Roman world and the Senate bestowed upon him the name of Augustus in 27 BC. Octavian, now Augustus, would be the first Roman Emperor and would transform the oligarchic Republic into the autocratic Roman Empire.
The last Republican Civil War would mark the beginning of the Pax Romana, a period of relative internal peace and stability." [Wikipedia]