Sparta Seemed Too Small to Defeat the AtheniansIt has been claimed that the Spartan elite had grown so small it avoided fighting whenever possible. For instance, although its role was crucial, Sparta's appearance in the battles against the Persians in the Persian Wars was often late, and even then, reluctant.
"[The Spartans] had obviously committed themselves to assisting the Athenians in any clash with the Persians. Nevertheless, when the news arrived that the Persians had landed at Marathon on the Attic coast in 490, the Spartans were careful to be celebrating an obligatory religious festival that prevented them from coming immediately to the Athenians' defense."
Greek Society, by Frank J. Frost
Spartans Were Outnumbered by Their Helots (Serfs)When we think of Sparta and the Lacedaemonians, we usually envision a regimented, fearless, obedient, upper-class fighter or Spartiate, obviously superior militarily to the sensual, democracy-loving, philosophy-pursuing Athenians. But there weren't many of these Spartans in Greece. Even in Sparta, they were in the minority. Not only were there more of the serf-like helots than privileged Spartiates, but the ranks of those between the helots and Spartiates -- the non-serf, lower-class -- would increase, each time a citizen Spartiate fell out of the upper class because he failed to make his required contribution to this early communist society.
Why then was Sparta victorious over Athens in the Peloponnesian Wars, the wars that followed the battles with Persia?
Outside Events Led to the Spartan Rise to PowerIn 404 B.C. the Athenians surrendered to the Spartans -- unconditionally. This marked the end of the Peloponnesian Wars. Defeating Athens had not been a foregone conclusion, but Sparta emerged victorious. There were many reasons, including, especially, the tactical errors of the Athenian leaders Pericles and Alcibiades(*), and the speculated about, but still unidentified plague that devastated Athens (because the people from the countryside had all come together with the city dwellers to live in a confined area within the walls "for safety" -- a situation highly conducive to the spread of an epidemic) and killed Pericles. Sparta had entered the 1st Peloponnesian War to aid an ally, Corinth, after Athens had taken the side of Corcyra (Corfu).
Copying Athens, Sparta Built Up Its NavySparta's newly created naval fleet was also important in achieving victory over Athens. Previously Athens had been as strong in its navy as Sparta had been weak. In the decisive Persian War Battle of Salamis, it was Athens that had used its navy under Themistocles to repulse the Persians. Although pretty much all of Greece has the sea to one side, Sparta fronts a dangerous stretch of the Mediterranean -- a situation that had previously prevented her from becoming a sea power. (See Geography of Greece.) During the 1st Peloponnesian War, Athens had kept Sparta at bay by blockading the Peloponnese with its navy. During the 2nd Peloponnesian War, Darius II, king of Persia, supplied the Spartans with the capital to build a capable naval fleet. And so, with a large enough navy, allies, manpower less ravaged by disease, and other advantages, Sparta defeated Athens.
The Spartans in PowerThe 33 years following the surrender of Athens were known as the "Spartan hegemony." The governments of oligarchic Sparta and democratic Athens were at opposite political extremes. Other poleis were probably run by governments somewhere between the two. Spartan rule chafed so much that, in the end, even Sparta's allies turned on her.(**)
(*)Under Alcibiades as strategos, the Athenians planned to try to deprive the Spartans of their food supply by cutting it at its source, Magna Graecia. But Alcibiades was recalled because of vandalism (mutilation of the herms) he was implicated in. He escaped and fled to Sparta where he revealed the Athenian plan.
The Peloponnesian War
Both Athens and Sparta fought a war of attrition. After Pericles died of the plague, Nicias took over and arranged a truce until the colorful character Alcibiades persuaded the Athenians to attack the Greek city-states in Sicily. The Athenian strength had always resided in her navy, but much of the Athenians' fleet was destroyed in this foolish campaign. Still, the Athenians were able to fight effective naval battles until after the Persians had lent their support to Sparta. Then Athens' entire naval force was destroyed. Athens surrendered to the great (but soon to be disgraced) Spartan general Lysander.
(**)The Spartan Hegemony
Richard Hooker's page explaining the way the Spartans used their period of dominance in Greece to their disadvantage by engaging in an ill-advised alliance with the Persians and then by Agesilaus' unprovoked attack on Thebes. The hegemony ended when Athens joined Thebes against Sparta.
Ancient History Sourcebook: 11th Brittanica: Sparta
The history of the Spartans from prehistory to the middle ages. Explains how ill-suited the Spartans were to rule the Greek world and how they surrendered hegemony to the Thebans.