In pursuance of the treaty, the Lacedaemonians withdrew their harmosts and garrisons, whilst the Athenians recalled their fleet from the Ionian sea. Only one feeling prevailed at Sparta - a desire to crush Thebes. This city was regarded as doomed to destruction; and it was not for a moment imagined that, single- handed, she would he able to resist the might of Sparta. At the time when the peace was concluded Cleombrotus happened to be in Phocis at the head of a Lacedaemonian army; and he now received orders to invade Boeotia without delay. The Thebans on their side, were equally determined on resistance. The two armies met on the memorable plain of Leuctra, near Thespiae. The forces on each side are not accurately known, but it seems probable that the Thebans were outnumbered by the Lacedaemonians. The military genius of Epaminondas, however, compensated any inferiority of numbers by novelty of tactics. Up to this time Grecian battles had been uniformly conducted by a general attack in line. Epaminondas now first adopted the manoeuvre, used with such success by Napoleon in modern times, of concentrating heavy masses on a given point of the enemy's array. Having formed his left wing into a dense column of 50 deep, so that its depth was greater than its front, he directed it against the Lacedaemonian right, containing the best troops in their army, drawn up 12 deep, and led by Cleombrotus in person. The shock was terrible. Cleombrotus himself was mortally wounded in the onset, and with difficulty carried off by his comrades. Numbers of his officers, as well as of his men, were slain, and the whole wing was broken and driven back to their camp. The loss of the Thebans was small compared with that of the Lacedaemonians. Out of 700 Spartans in the army of the latter, 400 had fallen; and their king also had been slain, an event which had not occurred since the fatal day of Thermopylae.

The victory of Leuctra was gained within three weeks after the exclusion of the Thebans from the peace of Callias. The effect of it throughout Greece was electrical. It was everywhere felt that a new military power had arisen - that the prestige of the old Spartan discipline and tactics had departed. Yet at Sparta itself though the reverse was the greatest that her arms had ever sustained, the news of it was received with an assumption of indifference characteristic of the people. The Ephors forbade the chorus of men, who were celebrating in the theatre the festival of the Gymnopaedia, to be interrupted. They contented themselves with directing the names of the slain to be communicated to their relatives, and with issuing an order forbidding the women to wail and mourn. Those whose friends had fallen appeared abroad on the morrow with joyful countenances, whilst the relatives of the survivors seemed overwhelmed with grief and shame.

Immediately after the battle the Thebans had sent to Jason of Pherae in Thessaly to solicit his aid against the Lacedaemonians. This despot was one of the most remarkable men of the period. He was Tagus, or Generalissimo, of all Thessaly; and Macedonia was partially dependent on him. He was a man of boundless ambition, and meditated nothing less than extending his dominion over the whole of Greece, for which his central situation seemed to offer many facilities. Upon receiving the invitation of the Thebans, Jason immediately resolved to join them. When he arrived the Thebans were anxious that he should unite with them in an attack upon the Lacedaemonian camp; but Jason dissuaded them from the enterprise, advising them not to drive the Lacedaemonians to despair, and offering his mediation. He accordingly succeeded in effecting a truce, by which the Lacedaemonians were allowed to depart from Boeotia unmolested.

According to Spartan custom, the survivors of a defeat were looked upon as degraded men, and subjected to the penalties of civil infamy. No allowance was made for circumstances. But those who had fled at Leuctra were three hundred in number; all attempt to enforce against them the usual penalties might prove not only inconvenient, but even dangerous; and on the proposal of Agesilaus, they were, for this occasion only, suspended. The loss of material power which Sparta sustained by the defeat was great. The ascendency she had hitherto enjoyed in parts north of the Corinthian gulf fell from her at once, and was divided between Jason of Pherae and the Thebans. Jason was shortly afterwards assassinated. His death was felt as a relief by Greece, and especially by Thebes. He was succeeded by his two brothers, Polyphron and Polydorus; but they possessed neither his ability nor his power.

The Athenians stood aloof from the contending parties. They had not received the news of the battle of Leuctra with any pleasure, for they now dreaded Thebes more than Sparta. But instead of helping the latter, they endeavoured to prevent either from obtaining the supremacy in Greece, and for this purpose called upon the other states to form a new alliance upon the terms of the peace of Antalcidas. Most of the Peloponnesian states joined this new league. Thus even the Peloponnesian cities became independent of Sparta. But this was not all. Never did any state fall with greater rapidity. She not only lost the dominion over states which she had exercised for centuries; but two new political powers sprang up in the peninsula, which threatened her own independence.