Repercussions

Athens's defeat ended the democracy that had built the Parthenon. Sparta installed thirty pro-Spartan oligarchs who executed approximately 1,500 citizens in eight months of political terror. Democratic exiles organised resistance and restored the democracy in 403 BC under an amnesty — one of the first general political amnesties in Western history. Democracy continued, but Athens never regained its imperial power or pre-war confidence. The trauma of the Thirty Tyrants poisoned Athenian politics for a generation and led directly to the trial and execution of Socrates in 399 BC.

Socrates was tried and executed in 399 BC — five years after Athens's defeat — on charges of impiety and corrupting youth. The charges were political cover for resentment of his association with Alcibiades and the Thirty Tyrants' connections to his circle. His student Plato, traumatised by the execution, concluded that democracy was fundamentally irrational and spent his life building a philosophical alternative. The Republic, the Apology, the Symposium — all of Western philosophy begins with one old man drinking hemlock to demonstrate that an examined life is worth dying for.

Sparta won the Peloponnesian War and proved immediately incapable of exercising the hegemony it had won. Lysander's system of installing pro-Spartan oligarchies across Greece was cruel and unpopular; his personal ambitions alarmed even Sparta's kings. Persian support was withdrawn when Sparta allied with Cyrus the Younger against Artaxerxes. Athens recovered its democracy within a year. Within thirty years, the Theban general Epaminondas — using tactical innovations that the Battle of Delium had foreshadowed — destroyed a Spartan army at Leuctra in 371 BC, killing 400 of the 700 remaining Spartan citizens and ending Spartan military power permanently.

The Peloponnesian War destroyed the balance of power that had allowed Greek city-states to maintain their independence. Athens never recovered its empire; Sparta lost its military reputation at Leuctra; Thebes's supremacy lasted barely a decade before Macedon absorbed it. When Philip II of Macedon defeated Athens and Thebes at Chaeronea in 338 BC, there was no power left in Greece capable of stopping him. His son Alexander then carried Greek culture to the ends of the known world — but as a Macedonian empire, not as a system of free self-governing city-states. The Peloponnesian War ended the classical era of Greek independence.

The supreme irony of the Peloponnesian War is that it enabled the very outcome both Athens and Sparta had fought to prevent: domination of Greece by a single power. That power was not either of them. Philip II and then Alexander the Great used Macedonian manpower, money, and innovative combined-arms tactics to overrun a Greece weakened by a generation of self-destruction. Alexander then achieved what no Greek of the Persian Wars generation could have imagined: the complete conquest of the Persian Empire that had twice invaded Greece. The world Pericles made possible, Athens's Peloponnesian War destroyed — and Alexander rebuilt on a continental scale.

Thucydides wrote that the Peloponnesian War was caused by 'the growth of Athenian power and the alarm which this caused in Sparta' — a diagnosis of structural rivalry between a rising power (Athens) and an established hegemon (Sparta) that political scientists now call 'the Thucydides Trap.' Harvard professor Graham Allison identified 16 cases in the past 500 years where a rising power challenged a ruling one; in 12 of them, the result was war. Thucydides' analysis, written 2,400 years ago, remains the foundational text of international relations theory.

Thucydides' account of the Plague of Athens in 430 BC is the first detailed description of epidemic social breakdown in Western literature. He described not just the medical symptoms but the social consequences: the abandonment of burial rites, the collapse of religious observance, the lawlessness of people who expected to die before facing consequences. The plague killed Pericles — removing the one man who might have maintained strategic discipline in Athens — and may have killed up to a third of the population, particularly the rowers who were Athens's naval edge. Its public health description was so accurate that epidemiologists have spent decades trying to identify the disease (typhoid fever is currently the leading candidate).

The Peloponnesian War ended not just because of Sparta's military superiority but because Persia — the enemy that the Greek wars were supposed to have permanently contained — provided the gold that built Sparta's fleet. The Persian prince Cyrus the Younger gave Lysander unlimited financial support after 407 BC; it was this money, and specifically these Persian rials and darics, that hired the rowers who won Aegospotami. The Persian Wars had been fought to keep Persia out of Greek affairs; fifty years later, Persia was deciding who ruled Greece. It was the supreme vindication of Pericles' warning that Athens must never fight a war it couldn't win before Persia became involved.