So how's about we discuss the possibility that, in an ATL where Cyrus the Younger defeats his brother Artaxerxes II, the 10,000 Greek mercenaries he brings perform so well that he decides to award them with land in Mesopotamia.
This leads to a not insignificant state of Sparta-influenced warriors in Mesopotamia that can possibly make or break kings, and a stronger Achaemenid Persia (Cyrus was a warlike go-getter, whereas OTL's winner was Artaxerxes, who focused too much on the pleasures of rule, ignoring the duties).
Is this a possibility/would Cyrus allow the Greeks to settle in Mesopotamia?