After the assassination, Mark Antony formed an alliance with Caesar's adopted son and great-nephew, Gaius Octavian. Along with Marcus Lepidus, they formed an alliance known as the Second Triumvirate. They held powers that were nearly identical to the powers that Caesar had held under his constitution. As such, the Senate and assemblies remained powerless, even after Caesar had been assassinated. The conspirators were then defeated at the Battle of Philippi in 42 BC. Eventually, however, Antony and Octavian fought against each other in one last battle. Antony was defeated in the naval Battle of Actium in 31 BC, and he committed suicide with his lover, Cleopatra. In 29 BC, Octavian returned to Rome as the unchallenged master of the Empire and later accepted the title of Augustus ("Exalted One"). He was convinced that only a single strong ruler could restore order in Rome.

Who was soon allied with Caesar's adopted son following his death?