The consequence of the Peloponnesian War on ancient Greece was a significant weakening of the city-states involved, particularly Athens and Sparta. The war, fought between 431 and 404 BC, resulted in a Spartan victory but left both sides economically drained and politically unstable. The conflict exacerbated rivalries and divisions among Greek city-states, leading to the eventual rise of Macedonian power under Philip II. The weakened state of Greece created an opportunity for external conquest, notably the invasion by Alexander the Great, and marked the end of the classical Greek era of unity and cultural flourishing.