THE PELOPONNESIAN WAR: THE SPARTAN AND THE THEBAN SUPREMACY. 1. THE PELOPONNESIAN WAR (431-404 B.C.). CAUSES OF THE WAR.--During the closing years of the life of Pericles, the growing jealousy between Athens and Sparta broke out in the long struggle known as the Peloponnesian War. Pericles had foreseen the coming storm: "I descry war," said he, "lowering from the Peloponnesus." His whole later policy looked toward the preparation of Athens for the "irrepressible conflict." The immediate causes of the war were, first, the interference of Athens, on the side of the Corcyræans, in a quarrel between them and their mother city Corinth; and secondly, the blockade by the Athenians of Potidæa, on the Macedonian coast. This was a Corinthian colony, but it was a member of the Delian league, and was now being chastised by Athens for attempted secession. Corinth, as the ever-jealous naval rival of Athens, had endeavored to lend aid to her daughter, but had been worsted in an engagement with the Athenians. With affairs in this shape, Corinth, seconded by other states that had causes of complaint against Athens, appealed to Sparta, as the head of the Dorian alliance, for aid and justice. The Spartans, after listening to the deputies of both sides, decided that the Athenians had been guilty of injustice, and declared for war. The resolution of the Spartans was endorsed by the Peloponnesian confederation, and apparently approved by the Delphian oracle, which, in response to an inquiry of the Spartans as to what would be the issue of the proposed undertaking, assured them that "they would gain the victory, if they fought with all their might." COMPARISON OF THE RESOURCES OF SPARTA AND OF ATHENS.--The resources of Hellas were, at the outbreak of the war, very evenly divided between the two parties. With Sparta were all the states of the Peloponnesus, save Argos and Achaia, while beyond the Isthmus the Boeotian League, headed by Thebes, and other states were her allies. Together, these states could raise a land force of sixty thousand men, besides a considerable naval armament, Corinth being especially strong in ships. Athens commanded all the resources of the subject cities--about three hundred in number, with twice as many smaller towns--of her great maritime empire. Her independent allies were Chios, Lesbos, Corcyra, and other states. Of course the chief strength of Athens lay in her splendid navy. THE BEGINNING: ATTACK UPON PLATÆA BY THE THEBANS.--The first act in the long and terrible drama was enacted at night, within the walls of Platæa. This city, though in Boeotia, was under the protection of Athens, and would have nothing to do with the Boeotian League.