The Peloponnesian War (431–404 BC) was an ancient Greek war fought by Athens and its empire against the Peloponnesian League led by Sparta. Historians have traditionally divided the war into three phases. In the first phase, the Archidamian War, Sparta launched repeated invasions of Attica, while Athens took advantage of its naval supremacy to raid the coast of the Peloponnese and attempt to suppress signs of unrest in its empire. This period of the war was concluded in 421 BC, with the signing of the Peace of Nicias. That treaty, however, was soon undermined by renewed fighting in the Peloponnese. In 415 BC, Athens dispatched a massive expeditionary force to attack Syracuse in Sicily; the attack failed disastrously, with the destruction of the entire force, in 413 BC. This ushered in the final phase of the war, generally referred to either as the Decelean War, or the Ionian War. In this phase, Sparta, now receiving support from Persia, supported rebellions in Athens' subject states in the Aegean Sea and Ionia, undermining Athens' empire, and, eventually, depriving the city of naval supremacy. The destruction of Athens' fleet at Aegospotami effectively ended the war, and Athens surrendered in the following year. Corinth and Thebes demanded that Athens should be destroyed and all its citizens should be enslaved, but Sparta refused.
The Peloponnesian War reshaped the ancient Greek world. On the level of international relations, Athens, the strongest city-state in Greece prior to the war's beginning, was reduced to a state of near-complete subjection, while Sparta became established as the leading power of Greece. The economic costs of the war were felt all across Greece; poverty became widespread in the Peloponnese, while Athens found itself completely devastated, and never regained its pre-war prosperity. The war also wrought subtler changes to Greek society; the conflict between democratic Athens and oligarchic Sparta, each of which supported friendly political factions within other states, made civil war a common occurrence in the Greek world.
The Thirty Years' Peace was first tested in 440 BC, when Athens' powerful ally Samos rebelled from its alliance with Athens. The rebels quickly secured the support of a Persian satrap, and Athens found itself facing the prospect of revolts throughout the empire. The Spartans, whose intervention would have been the trigger for a massive war to determine the fate of the empire, called a congress of their allies to discuss the possibility of war with Athens. Sparta's powerful ally Corinth was notably opposed to intervention, and the congress voted against war with Athens. The Athenians crushed the revolt, and peace was maintained.
When the Athenians and Spartans found themselves at war with one another in 431 B.C.E., both sides believed a conclusion would come quickly- a delusion common to many of history's pivotal contests. Instead, the war dragged on for twenty-seven years. Thucydides, writing about it in exile, recalled that he knew from the time of its outbreak that it was going to be " the greatest war in history," amounting to the first world war. He also meant that it was the worst, so devastating to both sides that it destroyed the Greeks' proud heritage of freedom. By h
Athens and Sparta, both powerful Greek city-states, had fought as allies in the Greco-Persian Wars between 499 and 449 B.C. In the wake of the Persian retreat, however, Athens grew more powerful and tensions rose, escalating into nearly three decades of war. Sparta emerged victorious, while the constant fighting left Athens bankrupt, exhausted and demoralized. Neither city-state regained the military strength they once had.