The Peloponnesian War between Sparta and Athens lasted 27 years, from 431 to 404 BCE.
The war began when tensions between Athens and Sparta’s alliance developed into open conflict. Athens possessed a powerful navy and relied on its empire, while Sparta and its allies were strongest on land. The conflict was not continuous in the same form: the Peace of Nicias created an interval of uneasy peace from 421 to 415 BCE before fighting resumed.
Major episodes included the Spartan invasions of Attica, the Athenian disaster in Sicily, and the final naval campaigns funded partly by Persia. Sparta’s victory at Aegospotami in 405 BCE destroyed the Athenian fleet and made surrender unavoidable. Athens capitulated in 404 BCE.
The conflict is often called the Peloponnesian War because Sparta led the Peloponnesian League. Its outcome ended Athens’ imperial dominance but did not create lasting Spartan stability; Thebes later defeated Sparta at Leuctra in 371 BCE.