The Athenian Empire was a powerful alliance of Greek city-states led by Athens during the 5th century BCE. It emerged after the Persian Wars, when Athens took the lead in forming the Delian League to protect against future invasions. Member states contributed money or ships, which helped Athens grow wealthy and expand its influence across the Aegean Sea. As the empire flourished, Athens became a center of culture, philosophy, and democracy. However, its dominance led to tensions with other city-states, particularly Sparta. This rivalry eventually sparked the Peloponnesian War, which challenged the stability of the Athenian Empire and changed the course of Greek history.