The events around Potidaea had important consequences. The Corinthians saw the Athenians as trying to steal their colonies on both sides of Greece, Corcyra to the northwest and Potidaea to the northeast. The tenuous alliance that kept Athens and Sparta together in the early years after the Persian invasion was long gone. The Thirty Years’ Peace between the two leading cities had surprisingly held for some fourteen years, but it was only as binding as the good faith of the two sides made it. The Athenians had co-opted the Delian League, designed for defense of Greece against the Persians, as a private empire. They were now trying to take over colonies of other countries and eliminate all competition so to become undisputed masters of the sea. The Corinthians, who had their own merchant marine and commercial interests, realized that the Athenians were trying to freeze them out of trade and occupy their place. The delicate balance of power in Greece was being disrupted. The Corinthians called for a meeting in Sparta to urge their ally, the city with the most powerful army, to declare war on Athens. The city of Megara, suffering from a trade embargo by the Athenians, joined in, and the island of Aegina, an offshore neighbor and long an enemy of Athens, supported the Corinthians’ moves behind the scenes.
The Corinthian delegation spoke to the assembled allies of Sparta in late 432 and laid out their grievances. They complained of the aggressive and opportunistic nature of the Athenian state and warned that Sparta’s caution and conservatism was ill-equipped to deal with such an enemy. An Athenian delegation that happened to be present reminded the Spartans of Athens’ services to the Greeks in the Persian wars, compared their empire to Sparta’s hegemony over the Peloponnesus, and urged them to seek mediation. King Archidamus of Sparta characteristically recommended that negotiations take place before a declaration of war. Sthenelaidas, an ephor or tribune, called for a vote from the Spartan assembly, which voted by acclamation.[8] The shouts on both sides were comparable, so he ordered those for peace to stand on one side of the room, those for war on the other. The members rose and separated to opposite sides of the room. Those for war were clearly in the majority.[9]
The die was cast. Sparta declared war and was joined by her allies, most notably Corinth, the sea power, and Thebes, the great land power in Boeotia to the north of Athens. The Spartan confederation controlled most of the Peloponnesus to the south and Boeotia to the northwest of Athens, that is, the Greek heartland. Athens for her part controlled an empire of republics that made up the Delian League, which accounted for most of the Aegean rim and the Aegean islands; Thessaly in northern Greece was also an ally.
It was too late in the year to begin hostilities. In the spring a Spartan army would assemble in the Peloponnesus and invade Attica. More important, this would not be the usual small war of a couple of cities over boundaries or trading rights. It would be a war of one large bloc of Greek cities against another. It would be, in terms of the world the Greeks knew, a world war that would involve all of mainland Greece, most of the Greek islands, and eventually Sicily and the Persian Empire. No one present knew how long it would last or how devastating it would be. No one could foresee that it would stretch over some twenty-seven years, cost many thousands of lives, and cause immeasurable losses in property and prosperity. Yet there were, as perhaps there always are at the commencement of great wars, powerful leaders on both sides who viewed the conflict as inevitable, and believed their side had an advantage which they should pursue at this most opportune juncture of events. So the expedition that Socrates served in became not just a minor clash at the frontiers of civilization, but a turning point of history.
[8]. On the ephors, see Aristotle Politics 1270b6-35.
[9].Thucydides 1.66-87.