The Reasons for the Peloponnesian War in More Detail

The Peloponnesian War is the name given to the long series of conflicts between Athens and Sparta that lasted from 431 until 404 BC.

The reasons for this war are sometimes traced back as far as the democratic reforms of Cleisthenes, which Sparta always opposed. However, the more immediate reason for the war was Athenian control of the Delian League, the vast naval alliance that allowed it to dominate the Mediterranean Sea.

By 454 BC, when the League's treasury was transferred to Athens, the alliance had become an empire in all but name. Over the next two decades it began treating its fellow members as ruled subjects rather than partners, and fought several short wars to force members who wanted to leave the League to rejoin it.

In 433 BC, when Athens signed a treaty of mutual protection with Corcyra (modern-day Corfu) - one of the few other city-states with a major navy of its own - Sparta and its allies interpreted the move as an act of provocation. A year later Sparta cancelled its peace treaty with Athens.

Then in 431 BC a contingent of soldiers from Thebes, Sparta's ally, tried to seize control of a town called Potidea. Caught and imprisoned, the townspeople put all 200 members of the advanced party to death. When a messenger from Athens arrived the next day to persuade the town against such a rash act, it was too late. The war had begun.