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How did Sparta defeat Athens in the Peloponnesian War?

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The Parthenon stands atop the Acropolis hill in Athens, Greece, surrounded by ancient stone walls and ruins, with city buildings and a distant hill in the background. — ancient Greek civilization The Acropolis, Athens.

Sparta defeated Athens in the Peloponnesian War primarily by overcoming Athenian naval superiority and cutting off the city's supply lines.1

While Athens was dominant at sea and Sparta was stronger on land, the war's turning point occurred during the second period of fighting. After a disastrous Athenian expedition to Sicily (415–413 BCE) resulted in the destruction of their army and navy, Athens faced severe political turmoil and military setbacks.21

The final blow came in 405 BCE at the Battle of Aegospotami. The Spartan fleet, commanded by Lysander and bolstered by critical financial and naval aid from Persia, surprised and destroyed the Athenian navy. Following this victory, Sparta established an impenetrable blockade around Athens. Starved and unable to secure its food supply, Athens was forced to capitulate in 404 BCE, marking the end of the war and the eclipse of the Athenian golden age.31