The Peloponnesian War was a pivotal conflict in ancient Greece, pitting Athens against Sparta and their respective allies. This prolonged struggle, lasting from 431 to 404 BCE, reshaped the Greek world and marked the end of Athens' golden age. The war's origins stemmed from growing tensions between Athens and Sparta, fueled by Athenian imperialism and Spartan fears of losing dominance. Key events included the Plague of Athens, the disastrous Sicilian Expedition, and the final Spartan victory at Aegospotami, leading to Athens' surrender and decline.