The news of the battle of Issus in 333 BC, however, put a check upon their plans. He sent his brother Agesilaus (unrelated to the Spartan monarchs of the same name) with instructions to sail with them to Crete, that he might secure that island for the Spartan interest. In this he seems in a great measure to have succeeded.
Two years afterwards (331 BC), the Greek states which were in league against Alexander seized the opportunity of the disaster of Zopyrion and the revolt of the Thracians, to declare war against Macedonia. Agis was invested with the command, and with the Lacedaemonian troops, and a body of 8000 Greek mercenaries, who had been present at the battle of Issus, gained a decisive victory in the Peloponnese over a Macedonian army under Coragus. Having been joined by the other forces of the league (Elis, Achaea except Pellene, and Arcadia, although, fatefully, Athens declined) he laid siege to Megalopolis. The city held out until Antipater came to its relief, when a battle ensued, in which Agis was defeated and killed, a good Spartan death, but one that left Sparta almost irretrievably weakened. This happened about the time of the battle of Gaugamela in 331 BC.