The Peloponnesian War (Ancient Greek: Πόλεμος τῶν Πελοποννησίων, romanised: Pólemos tō̃n Peloponnēsíōn), was fought in the Eastern Mediterranean between the Athenian-led Delian League and the Spartan-led Peloponnesian League from 431 to 404 BC for hegemony over Ancient Greece. Initially inconclusive, the intervention of the Persian Empire in support of Sparta in 413 BC allowed the Spartan coalition to decisively defeat Athens, beginning a period of Spartan hegemony over Greece.
The war consists of four related conflicts which have traditionally been combined into one. The opening phase, called the Ten Years' War or the Archidamian War, began in 431 BC when the Spartan king Archidamus II invaded Attica with his army. After successive Spartan invasions of Attica and Athenian raiding of the Peloponnese, Athens gained the upper hand at Sphacteria in 425 BC, but lost it after a defeat by Thebes at Delium in 424 BC. With both city-states exhausted from years of fighting, the Peace of Nicias was signed in 421 BC. The second phase, the Argive War, was fought between 419 and 416 BC. It was a proxy war that pitted Sparta against its Peloponnesian rivals, led by Argos and supported by Athens. The Argive alliance was defeated at the battle of Mantinea of 418 BC, restoring Spartan hegemony over the Peloponnese. The third phase, the Sicilian Expedition, was an attempt by Athens to conquer the Spartan-allied Syracuse. Fought between 415 and 413 BC, the expedition ended in defeat for Athens and the destruction of most of its navy.
