A Tense Peace
The Peace of Nicias was probably doomed from the start as it wasn’t popular with Sparta’s allies. The Boeotians and Corinth were against it; especially the part which allowed Sparta and Athens to make changes without consulting their allies. The warring states created an unexpected alliance; each agreed to come to one another’s aid if they were attacked. Sparta initiated this agreement due to the fear of the state of Argos forming a powerful alliance once its peace treaty with Sparta expired.
Although the war itself did not restart for another six years, the ‘peaceful’ period consisted of various skirmishes involving the other city states. In 420 BC, Boeotia formed a new alliance with Sparta whereas Athens allied itself with Argos, Mantinea, and Elis. The two alliances came close to battle on several occasions, but there was no major battle for a couple of years.
The Athenian alliance encountered an enormous Spartan army under King Agis II at the Battle of Mantinea in 418 BC. The Athenian-allied army lost well over 1,000 men while Spartan losses were below 300 according to historian Thucydides. It was a crushing defeat that helped remind the rest of the Greek world that the Spartans were still the best warriors in the region. Even though the enemies had clashed at the Battle of Mantinea, the Peace of Nicias had technically not been breached, so the tense peace continued for a few more years.
Both states were guilty of some terrible crimes in this period. In 417/16 BC, the Spartans executed all the citizens of Hysiai while the Athenians murdered the citizens of Melos. The following three years was a period of stalemate as both states carried out minor actions that didn’t breach the peace treaty. The defeat at Mantinea did nothing to dent Athenian confidence, so it answered a call for help from some of the Greek cities of Sicily. Athens had allies on the island such as the Segestans, and they tried to get Athenian help by suggesting that the Syracusans would take control of Sicily thus helping Sparta.