371 BC

By place

Greece

• A fresh peace congress is summoned at Sparta. At the peace conference, the Spartan King Agesilaus II refuses to allow the Thebans to sign the treaty on behalf of all Boeotia. The Theban Epaminondas, who is boeotarch, maintains Thebes' position, even when it leads to the exclusion of Thebes from the peace treaty.
• Thebes' actions at the peace congress lead to a war between Sparta and Thebes. The Spartans have an army stationed on Thebes' western frontier, waiting to follow up their diplomatic success by a crushing military attack. However, at the Battle of Leuctra, the Theban generals, Epaminondas and Pelopidas, win a decisive victory over the Spartans under the other Spartan king, Cleombrotus I. Epaminondas wins the battle with a tactical innovation which involves striking the enemy first at their strongest, instead of their weakest, point, with such crushing force that the attack is irresistible. As a result of this battle, the Boeotian federation is saved.
• Athens does not welcome the Theban victory, fearing the rising aggressiveness of Thebes. After the Theban victory, the old alliance between the Persians and the Thebans is restored.
• With the unexpected defeat of Sparta by the Thebans, the Arcadians decide to re-assert their independence. They rebuild Mantinea, form an Arcadian League and build a new federal city, Megalopolis.
• Agesipolis II succeeds his father Cleombrotus I as king of Sparta.

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Astronomy

• It is suggested that the original comet associated with the Kreutz Sungrazers family of comets passes perihelion at this time. It is thought to have been observed by Aristotle and Ephorus during this year.