The King's Peace (387 BC) a.k.a. The Peace of Antalcidas (after the Spartan diplomat who travelled to Susa to negotiate a treaty with Artaxerxes II Mnemon (r. 404 – 358 BCE) returned Persian control of Asia Minor, Ionia and parts of the Aegean Sea.
At the end of the Corinthian War, many cities across the Aegean had fallen under Athenian control. Since the Athenian gains threatened Persian interests, Artaxerxes switched his support from Athens and her allies in Thebes, Corinth and Argos to Sparta.
Antalcidas' Spartan fleet of ninety ships moved into the Hellespont, threatening the trade routes that brought grain from the Black Sea to Athens.
A similar move had brought about the Athenians' disastrous defeat in 404 BCE. With Athens forced to negotiate, Thebes, Corinth, and Argos were unwilling to continue hostilities on their own. At a peace conference in Sparta, all the belligerents in the Corinthian Wars accepted terms laid down by Artaxerxes.
While the peace guaranteed Greek autonomy in exchange for recognition that their cities in Asia Minor and the islands of Cyprus belonged to Persia, in effect, the treaty placed Greece under Persian suzerainty.
It also allowed the Spartans to exploit a mandate to protect and enforce the peace to launch campaigns against centres that they saw as political threats.
By granting Sparta powers that would infuriate the other Greek city-states if they used them, the treaty ensured a state of near-constant warfare that lasted until the rise of Macedonian power under Philip II and Alexander the Great.
Sources:
Simon Hornblower, Antony Spawforth, and Esther Eidinow (eds), The Oxford Classical Dictionary
M. C. Howatson (ed) , The Oxford Companion to Classical Literature
John Roberts (ed.), Oxford Dictionary of the Classical World
Wikipedia