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The Peloponnesian War was one of the greatest conflicts in the Classical World. It was a conflict that involved the Athenian Empire and its allies in a brutal struggle with Sparta and the Peloponnesian League. The war lasted almost three decades (431-404 BCE) and was to change the Greek world. Perhaps one of the most important events in this was Athens Sicilian Expedition (413-415 BCE). This was an attempt by the Athenians to conquer the island of Sicily. This expedition which resulted in a disastrous Athenian defeat is usually seen as a turning point in the war. Prior to the expedition, Athens could hold its own against Sparta and it could maintain its Empire. However, the disastrous Sicilian expedition weakened Athens severely and exacerbated domestic tensions in its society that ultimately led to the defeat of the City and the loss of its Empire.

==Background==

In the aftermath of the Second Persian Invasion (480-479 BCE), Athens emerged as a great power in Greece. The city-state and Sparta had led the Greek world against the Persians. In the aftermath of the Persian defeat, Sparta for internal reasons ended its participation in the war against the Persians. Athens continued the struggle against Persia and established the League of Delos. The Athenians eventually turned the League of Delos into an Empire. It could do this because it had a huge navy. Sparta grew increasingly worried and suspicious of Athens. When Athens issued the Megarian Decree, Sparta responded by invading Attica. This led to total war between Athens and Sparta. Athens followed the strategy of Pericles. The Periclean strategy urged Athens to avoid a land war with Sparta and to concentrate on its navy and to avoid other entanglements. Despite the death of Pericles early in the war, during a plague, his strategy was followed for many years. Sparta and its allies were unable to defeat Athens and indeed the Athenians inflicted a humiliating defeat on Sparta on the island of Pylos. This led to a truce between the two most powerful Greek city-states and this eventually to the so-called Peace of Nicias. Athens was as powerful as ever and it seemed that if it followed Pericles strategy that it was invincible. This was all to change with the Sicilian Expedition.