Lysander captures almost the whole Athenian fleet on the beach at Aegospotami. When the news reaches Athens at night, no one sleeps.
It was at night that the Paralus arrived at Athens with tidings of the disaster, and a sound of wailing ran from Piraeus through the long walls to the city, one man passing on the news to another; and during that night no one slept
Without a fleet Athens could not import grain or reach its empire, so the defeat effectively ended the war. It left Sparta dominant across the Greek world, in an order that lasted more than thirty years.
Based on Wikipedia: Battle of Aegospotami
This effectively ended the war, since Athens could not import grain or communicate with its empire without control of the sea.
The Spartan victory at Aegospotami marked the end of 27 years of war, placing Sparta in a position of complete dominance throughout the Greek world and establishing a political order that would last for more than thirty years.