Philip II united the Greek city-states under Macedonian rule. His son, Alexander the Great, then conquered much of the known world including Greece, Egypt, Persia, and parts of India. Though Alexander's empire did not last after his death, it ushered in the Hellenistic Age where Greek culture spread widely. The empire's breakup led to periods of conflict but also stimulated advances in science, math, and philosophy that influenced later Roman and Western civilization.