In 43 B.C. Octavian, Antony and Marcus Aemilus Lepidus established the Second Triumvirate, a power-sharing agreement that divided up Rome’s territories among them, with Antony given the East, Lepidus Africa and Octavian the West. In 41 B.C. Antony began a romantic and political alliance with Cleopatra, queen of Egypt, which continued even after a Senatorial decree forced his marriage to Octavian’s sister Octavia Minor. Lepidus remained a minor figure until Octavian finally had him ousted after the triumvirate’s renewal in 37 B.C.
Antony’s affair with Cleopatra continued, and in 32 B.C. he divorced Octavia. In retaliation, Octavian declared war on Cleopatra. In the naval battle of Actium a year later, Octavian’s fleet, under his admiral Agrippa, cornered and defeated Antony’s ships. Cleopatra’s navy raced to aid her ally, but in the end the two lovers barely escaped. They returned to Egypt and committed suicide, leaving Octavian as Rome’s undisputed ruler."