Philip II of Macedon united the Greek city-states and built a powerful army. His son, Alexander the Great, seized power at age 20 after Philip's assassination. Alexander then conquered the vast Persian Empire and pushed his armies as far as India. However, his troops grew weary and he died of illness at age 32, leaving his generals to divide his empire among themselves. The Hellenistic period that followed saw the flowering of Greek culture and science throughout the Mediterranean and Middle East.