Peace of Nicias
In the spring of 432 BCE, during the first phase of the Peloponnesian War, several cities of Chalcidice broke away from the Athenian-dominated Delian League. The inhabitants of these cities abandoned them and moved to Olynthos in an act of synoecism, forming a single state and adopting the demonym "Chalcidians". Exactly what form it took is a matter of academic dispute. By the terms of the Peace of Nicias of 421 BCE, Athens and Sparta agreed that it should be broken up, but it seems clear that Athens failed to enforce this. Luckily for the Chalcidians, the attention of the two great powers was soon diverted away from them—indeed for this reason nothing is heard of Olynthos and the Chalcidians until 393/2 BCE— and the Spartan governors installed by Brasidas were soon withdrawn.