The Trap Closes

Thucydides wrote that the Peloponnesian War's real cause was 'the growth of Athenian power and the alarm this caused in Sparta' — a structural rivalry between a naval democracy and a land-based oligarchy that the peace of 446 BC had paused but not resolved. Fifty years after Salamis, Athens controlled an empire of 150–200 subject cities paying tribute, commanded the finest navy in the world, and was building monuments to its own glory with allied money. Sparta had watched this transformation with growing alarm and a growing sense that the Thirty Years Peace signed in 446 BC was simply buying Athens time to become irresistible.

The immediate causes were more mundane: competing alliances dragged both great powers into smaller conflicts they had not sought. Athens's intervention in the war between Corinth and Corcyra (Sybota, 433 BC) infuriated Corinth, Sparta's most important ally and trading partner. Athens's subsequent Megarian Decree — excluding Megara from Athenian-controlled markets, an economic stranglehold — felt to Sparta's allies like deliberate aggression. Corinth delivered an ultimatum at Sparta: either Sparta declared war on Athens, or Corinth would find new allies. Sparta's assembly voted for war, with the king Archidamus dissenting — warning that Athens was rich, had a fleet, and could endure a land war indefinitely.

Pericles' strategy was paradoxical: Athens would not fight on land. The Spartans could invade Attica and burn farms every summer; Athens would evacuate the countryside into the city, using its Long Walls to maintain connection with the port of Piraeus, and use its fleet and financial reserves to raid the Peloponnesian coast until Sparta ran out of money. It was a strategy of attrition, not victory — and it required Athenians to watch their olive groves and farmhouses burn year after year from behind their walls. The strategy was correct; it almost worked; then the plague destroyed it.