Artaxerxes II defeated and killed his brother, Cyrus the Younger, at the Battle of Cunaxa. He subsidized the Athenians, Thebans, and Corinthians in order to weaken the Spartans. This was one of the causes of the Corinthian War. In 386 BCE, Artaxerxes II betrayed his allies and came to an arrangement with Sparta in the Treaty of Antalcidas. The Greek cities of Ionia and Aeolis were given to Persia, while Sparta was given dominance on the Greek mainland.
The Egyptians revolted against Artaxerxes II at the beginning of his reign. In 373 he attempted unsuccessfully to reconquer Egypt. However, in his later years, he did manage to defeat a joint Egyptian–Spartan effort to conquer Phoenicia.
Artaxerxes II was the longest reigning of the Achaemenid kings.
In 1923, Dr. Jacob Hoschander wrote The Book of Esther in the Light of History, in which he posited that the events of the Book of Esther occurred during the reign of Artaxerxes II Mnemon. Other scholars identify Ahasuerus with Xerxes I, while others view the story as fictional.