The first Indo-Greek kingdom appeared circa 190 BCE may when the Greco-Bactrian king or (general for his father) Demetrios was busy in India, when his Indian possessions were divided between several kings, probably firstly in order to better govern them but then due to civil war. The term “Indo-Greek” is generally used because these kingdoms were almost always separated from Bactria and thus differed politically from the Greco-Bactrian kingdom.
This is a companion discussion topic for the original content at https://www.worldhistory.org/Indo-Greek/.