The Peace of Nicias was a treaty concluded in 421 B.C. between Sparta and Athens, during the Peloponnesian War. It was supposed to last for 50 years and cover the allies of each side, basically returning matters to their status before the war.
Allies were not consulted, and Spartan allies were unwilling to abide by the treaty.
Within seven years the Peace of Nicias was over and the Ionian War stage of the Peloponnesian War began with the Spartans breaking the treaty by occupying the Attic village of Declea.
The articles being, that the garrisons and towns taken on either side, and the prisoners should be restored, and they to restore the first to whom it should fall by lot, Nicias, as Theophrastus tells us, by a sum of money procured that the lot should fall for the Lacedaemonians to deliver the first.
Plutarch's Life of Nicias