There followed a period of uneasy peace between the Greek cities; of alliances projected, spoilt, effected; of recriminations and of diplomatic finesse, much of it wasted, all of it suspicious. Corinth and Boeotia refused stoutly to be parties to the Peace of Nicias. Neither Sparta nor Athens fulfilled its conditions, though the latter did surrender her Spartan prisoners in good faith. But she retained Pylos and Nisaea when Sparta professed her in ability to render up Amphipolis. And when, in July 420 B.c., a new Quadruple Alliance of Athens, Argos, Mantinea and Elis confronted a Spartan-Boeotian Alliance, the already moribund peace was doomed. This new democratic League was the work of one man at Athens, Nicias' political rival Alcibiades. Like Dis raeli entering on a public career about the age of 30, like him a man of brilliant talents and unbounded ambition he too in curred the undying distrust, even hatred, of the "respectable" majority of his fellow-citizens. Though henceforward to the end of the war Alcibiades' personality dominates Athenian life and politics, his unquestioned oratorical and military abilities could not surmount finally this handicap, and the party-animosity which he provoked was the final cause of Athens' downfall. This is Thucydides' own certain judgment.
Athens' "Third Offensive Strategy" was in idea her best.
Thanks to her new Peloponnesian allies she now threatened Sparta at home and made her rival stake her very existence upon the fortunes of a single fight. Then, to her salvation, Sparta dis covered in her King Agis the second of her great soldiers, one remarkable alike for strategical and for tactical ability. Taking the initiative, Agis assembled a powerful army at Phlius by a masterly piece of night-marching and descended from the north upon Argos. His Boeotian contingent failed him at the critical moment, and, forced to extricate the remainder from peril as best he could, he concluded a much misunderstood treaty with the enemy. A few months later Argos, at Alcibiades' insistence, denounced the treaty, and the allies, though including only a miserably inadequate Athenian contingent and weakened further by the selfish absence of the Eleans, threatened Tegea. Agis hastened to the rescue, and the resulting battle of Mantinea in August 418 B.C. was so striking a Spartan victory that by this, the greatest land battle of the war, Sparta redeemed her lost reputation. Argos henceforward ceased to count. That the Third Athenian Strategy was so disastrous. a failure was largely due to the blind folly of Alcibiades' political enemies, through whom he himself was not elected general in this the decisive year of its trial.