As soon as the Greco-Persian Wars ended, Sparta worried about the growing power of Athens, crowned by its victories against the Persians. Driven by Aegina and Corinth, it forbids the city to rebuild its walls, destroyed by the Persians. This does not prevent Athens from leaving the Pan-Hellenic League to go and found the Delos League. Sparta comes close to starting a war, but eventually gives up. Some tensions take place, but the relations between the two cities remain good until 462, when Sparta returns an Athenian contingent led by Cimon and come to assist him in full revolt of the Helots. It is then the rupture, sealed by the ostracism of the laconophile Cimon.
The actual hostilities began in 457, at the call of Corinth. There followed a series of victories and defeats for the two cities, which culminated in 451 in a 5-year peace, but relations remained tense. In 446, the revolt of Megara and Euboea revived the conflict:Sparta, at the head of united cities, ravaged Attica. King Pleistoanax is even accused of corruption, not having continued his offensive, and he is forced into exile. Finally, in 433, the affair of Corcyra began the Peloponnesian War.
Despite the fear of seeing Athens emerge from its status as a brilliant second to Sparta, not all Spartans are enthusiastic about the idea of a war that promises to be long, even if no one at the time imagined that it would last 27 years. The ephor Sthenelaïdas favors immediate war, but King Archidamos opposes him. The vote of the Assembly is uncertain:the exceptional procedure of voting by displacement must be used (see below). It is certain that it would have been better for Sparta to go to war in 440, before the defection of Samos, which deprived it of a powerful navy. The last negotiations between the two cities could probably have saved the peace, despite what Thucydides says.
In fact, the war is long, Pericles having had the idea of abandoning Attica to the regular looting of Sparta, to welcome its population in Athens itself, protected by the Long Walls. In 425, it was even the humiliating defeat of Sphacteria:120 Peers, mostly belonging to the great Spartan families, were taken prisoner on an islet. Sparta must surrender its fleet to recover its hoplites. It is a great trauma:for the first time, we see Equals surrender, without fighting to the end. In 421, the peace of Nicias is welcome.
However, tensions remain. Sparta and Athens even clashed, in 418, at Mantinea, outside the territory of the two cities. Athens concludes that Sparta has broken the treaties, and the war resumes in 415. Athens launches the Sicily expedition, which ends in disaster. The revolt of the Ionian cities of the league of Delos allowed Sparta to impose itself:in 404, besieged Athens capitulated.
Sparta forced it to raze the Long Walls, ten stadia on each side and enter the Peloponnese league. The Spartans hesitate, however, as to the form of government to give him. Everyone agrees on the need to end democracy, but do we need a radical oligarchy under Spartan tutelage, or a more moderate oligarchy without a Spartan garrison? King Lysander, the great architect of the victory over Athens, imposes the tyranny of the Thirty, but the other king, Pausanias I, then lets the Thirty fall and flee with their supporters, to support the moderate oligarchs who remained in Athens. However, on his return to Sparta, he was put on trial, and eight years after his acquittal, was condemned when Athens resumed arms against Sparta.