After the unconditional surrender of Athens at the end of the Peloponnesian War, Sparta became the undisputed major power among the Greek city-states. Stripped of its navy and its empire, Athens simply became just one more city under the political control of its more powerful neighbor in the south. This period in Greek history is called the Spartan hegemony, for although Sparta didn't rule the city -states of Greece as if it were an empire, Sparta did exercise considerable influence over the domestic and foreign decisions of these independent states: it exercised, then, hegemonic control over these states.
In Athens, the Spartan general who defeated the city, Lysander, pulled down the democratic government and established an oligarchy. Members of the democratic factions fled the city and raised armies in Corinth and in Thebes. The oligarchy ruled with an iron fist, often ordering summary executions of its political opponents (as Socrates tells us in The Apology); for this, the thirty members of the oligarchy were called "the Thirty Tyrants," or simply, "the Thirty." Eventually the Athenians were allowed by Sparta to return to a democratic constitution.
Sparta, meanwhile, vigorously went about establishing an empire of its own. Shortly after the defeat of Athens, they entered into an alliance with Cyrus, who claimed the Persian throne against his brother, Artaxerxes II, who occupied the throne. The Persians the the Greeks, under the leadership of Sparta, managed to make it all the way to the center of Mesopotamia and the capital itself, where Cyrus was killed. The Greeks escaped, but the Spartans soon entered into defensive alliances with the Greek city-states of Asia Minor.
The great figure of this age is Agesilaus, the king of Sparta from 396 to 360 BC. Agesilaus was an energetic and aggressive general who, though physically lame, was incomprehensibly physically brave whenever in battle. Soon the Spartan and Greek army was threatening Persia again, but the Persians destroyed the Spartan sea empire in 394 BC. The Spartans had been distracted by another war on the Greek mainland, the Corinthian War (395-387 BC), when Athens, Corinth, and Argos formed an alliance against Sparta. Athens rebuilt the walls of the city and its navy.
This war, like the Peloponnesian War, essentially accomplished nothing. In the end, all sides agreed to a peace established by the Persian king. Fearful of the Athenians, the Persian king put Sparta in charge of Greece, and Agesilaus promptly broke up the Corinthian alliance and any other alliances that didn't involve Sparta. From 387 BC onwards, Agesilaus and the Spartans closely controlled political decisions in the individual city-states and stacked their governments with individuals friendly to Sparta and its interests.
The period of Spartan hegemony saw the first years of the maturing of Greek philosophy. Socrates, who looms large as a principle foundation of Greek philosophy, had come to the end of his years when the Age of Pericles closed. He was put to death in 399 BC. However, his pupil, who more than anyone else is responsible for synthesizing earlier Greek philosophy int a single, overarching system, began his activities as a philosopher and teacher in these years. Based in Athens, his school, the Academy, would become the intellectual center of Greece in the decades to follow.
Agesilaus finally overstepped himself when he captured the city of Thebes without any provocation whatsoever. When he then turned on Athens, the Athenians allied themselves with the Thebans, and the Spartan control over Greece came to a final end in 371 BC.