The peace of Nicias was called a 'festering peace' by the Greek historian Thucidydes, and not without reason. One of the results of the peace of Nicias was that both parties would give back the conquered territory. However, the Spartan commander of Amphipolis refused to leave the city. Athens on its turn refused to return Phylos to Sparta. This, and other gaps in the peace gave the opposition of the peace of Nicias in Sparta, Corinth and Athens more space to start their political warfare.
Corinth tried to form an alternative Peloponessian League with Argos, which was a democratic city in those days. As a result did Sparta and Athens also attempted to find favour with Argos. Athens succeeded, most likely as it was also a democratic city, and the result was a defensive alliance between the two cities. A big battle place took place at Matinea in 418 between Sparta and a coalition, in which Athens took part, under the leadership of Argos. The outcome of this battle was uncertain for a long time, but finally Sparta managed to defeat its enemies. It not only resulted in a military victory for Sparta, but also a psychological one. After the loss of Phylos the faith in the invincible Spartan army was seriously damaged, but now it was completely restored again.
Athenian imperialistic tendencies.
The alliance between Athens and Argos had mostly been the work of Alcibiades. He was a nephew of Pericles, and since the death of his father he was adopted by the great Athenian leader. Alcibiades was also a brilliant politician and diplomat, and he would show his strategic capabilities during the war. However, his extravagant and unusual way of working, and his good relationship with the local aristocrats, were often reasons for the normal citizen not to trust him. This was not without reason as he had extraordinary capabilities, but he only used them to fulfil his own ambitions. After the failed co-operation between Athens and Argos Alcibiades became the spokesman of a group of people in Athens who wanted to further expand the Athenian empire. The imperialistic tendencies of this generation resulted in two catastrophic errors, which formed the end for Athens on the long term.
The first one was to support two Persian satraps in western Anatolia, Pissouthnes and then his son Amorges, who were in rebellion against the Persian king. Sparta had attempted to get money from the Persian empire during the Archidamian wars, but she failed as the Persian king did not have any real reason to support Sparta. Now Athens gave Persia a very good reason to support Sparta and its allies in their war with Athens.
The second disastrous error made by Athens to interfere in a conflict on Sicily. Syracuse was also involved in these conflicts, and as the most powerful Greek city in the west she had very good bonds with her mothercity Corinth. More than enough reason for the Athenian imperialists to form an expedition against Syracuse in 415, under the leadership of the not very harmonious couple Nicias and Alcibiades. Alcibiades was called back to Athens to justify himself for several occasions of iconoclasm just when the expedition had reached Sicily. Instead he fled to Sparta.
Sparta ends its isolationism.
In Sparta Alcibiades managed to become one of the counsellors of the kings, and he persuaded them to end their isolationism. Sparta made two decisions which were disastrous for Athens. The first one was that they sent their best general, Gylippus, with a small number of Spartiats to Syracuse. This proved to be the turning point in the war, as the inspiration which their appearance gave to the Syracusians, and the military capabilities of Gylippus resulted in the defeat of the Athenian expedition army. Athens lost 200 ships, and 4000 warriors. The few people who did survive were sold as slaves, while Nicias was sentenced to death in Syracuse. The lost battle at Sicily resulted in a shaking of confidence in Athens within her empire, but was even worse was the second advice of Alcibiades to Sparta. In 413 Sparta invaded Attica, and founded a permanent stronghold in the northern deme Decelea. The effect was that the Athenian silvermines in Laurium became isolated from Athens, that thousands of slaves deserted to the enemy, and that the import of food from Euboea was impossible for many years.