The Peloponnesian War was won by Sparta.
The Peloponnesian War ( 431 -- 404 BC ) was an ancient Greek war fought by Athens and its empire against the Peloponnesian League led by Sparta . Sparta . Between 431 and 404 BC , Sparta was the principal enemy of Athens during the Peloponnesian War , from which it emerged victorious , though at a great cost of lives lost .