The period from 464 B.C. to 404 begins with the great Spartan earthquake and ends with the conclusion of the Peloponnesian War.
The earthquake was a large magnitude event that caused significant loss of life in Sparta. Debate as to whether the army was seriously impacted by the loss of trainees and mature Spartiates is inconclusive, but it may have had an impact on Spartan thinking later. Immediately after the earthquake, the Messenian Helots took the opportunity and revolted. The length of their revolt is unclear, but it could have lasted several years. The Athenians sent a force of four thousand hoplites to assist Sparta after she made a request for aid, but that gesture only soured the relationship between the two Greek powers when the Athenians were not able to help prosecute the siege of the Messenian stronghold at Mount Ithome.
The Athenians were sent home, causing the reign of Cimon and the Athenian alliance with Sparta to come to an end. Cimon was exiled in favor of Pericles. The Athenians and Spartans went to war in 460 and fought half-heartily until 445 when they signed a thirty year peace treaty. The treaty lasted until 431, when the great Peloponnesian War began.
That war can be summed up as follows: Athens and Sparta fought to a draw between 431 and 422 when Athens sued for peace fearing defections of her allies. The war began again in 421. Two events mark this segment: the defeat of Athens and her allies at Mantinea in 418 and the failed Athenian attack on Syracuse in Sicily. In the third segment, starting in 413, Sparta invaded Attica and then allied itself with Persia who built ships for the Spartan Navy. Lysander, a brilliant Spartan admiral, defeated the Athenian allies at Aegosotami, the Athenians surrender, and the war finally came to an end.
Somewhere between the Messenian revolt and the Battle of Mantinea, Sparta changed the structure of its military and started to deploy Perioeci to fight along side Spartiates trained in the Agoge. Her hand may have been forced by the loses in the earthquake and closely fought battles such as Tanagra. The thirty year long Peloponnesian War also took its toll as the number of deaths exceeded Sparta’s ability to replace them. As strong as the Spartans were, even they couldn’t win without numbers.
Sparta reached the end of the Peloponnesian War as a “false victor”. The Athenians and their allies had surrendered, but Sparta was weak and in possession of Poleis it didn’t know how to control.