During Greece's Golden Age in the 5th century BC, Athens flourished in art, philosophy and democracy under the rule of Pericles. Pericles strengthened Athenian democracy and used money from the Delian League to fund architectural projects like the Parthenon. However, Athens' growing power led to conflicts and the Peloponnesian War with Sparta. Meanwhile, philosophers like Socrates, Plato and Aristotle asked fundamental questions, influencing Western thought. Later, Philip II and his son Alexander the Great conquered Greece and much of the known world, spreading Hellenistic culture across a vast empire from Egypt to India.