If the wars of the Delian League shifted the balance of power between Greece and Persia in favour of the Greeks, then the subsequent half-century of internecine conflict in Greece did much to restore the balance of power to Persia. The Persians entered the Peloponnesian War in 411 BC forming a mutual-defence pact with Sparta and combining their naval resources against Athens in exchange for sole Persian control of Ionia. In 404 BC when Cyrus the Younger attempted to seize the Persian throne, he recruited 13,000 Greek mercenaries from all over the Greek world, of which Sparta sent 700–800, believing they were following the terms of the defence pact and unaware of the army's true purpose. After the failure of Cyrus, Persia tried to regain control of the Ionian city-states, which had rebelled during the conflict. The Ionians refused to capitulate and called upon Sparta for assistance, which she provided, in 396–395 BC. Athens, however, sided with the Persians, which led in turn to another large-scale conflict in Greece, the Corinthian War. Towards the end of that conflict, in 387 BC, Sparta sought the aid of Persia to shore up her position. Under the so-called "King's Peace" that brought the war to an end, Artaxerxes II demanded and received the return of the cities of Asia Minor from the Spartans, in return for which the Persians threatened to make war on any Greek state that did not make peace. This humiliating treaty, which undid all the Greek gains of the previous century, sacrificed the Greeks of Asia Minor so that the Spartans could maintain their hegemony over Greece. It is in the aftermath of this treaty that Greek orators began to refer to the Peace of Callias (whether fictional or not), as a counterpoint to the shame of the King's Peace, and a glorious example of the "good old days" when the Greeks of the Aegean had been freed from Persian rule by the Delian League.