After the King's Peace of 387 BC, Sparta was anxious to re-establish its presence in northern Greece. In 385 BC, Bardylis and his Illyrians attacked Epirus instigated and aided by Dionysius I of Syracuse, in an attempt to restore the Molossian king Alcetas I of Epirus to the throne. When Amyntas sought Spartan aid against the growing threat of Olynthus, the Spartans eagerly responded. That Olynthus was backed by Athens and Thebes, rivals to Sparta for the control of Greece, provided them with an additional incentive to break up this growing power in the north. Amyntas thus concluded a treaty with the Spartans, who assisted him in a war against Olynthus. First it Spartan-Macedonian forces suffered two defeats but in 379 they managed to destroy Olynthus. He also entered into a league with Jason of Pherae, and assiduously cultivated the friendship of Athens. In 371 BC at a Panhellenic congress of the Lacedaemonian allies, he voted in support of the Athenians' claim and joined other Greeks in voting to help Athens to recover possession of Amphipolis.