Euthydemus I was, according to Polybius a Magnesian Greek.
His son, Demetrius, founder of the Indo-Greek kingdom, was therefore of Greek descent from his father at minimum.
But Seleucus Nicator gave them to Sandrocottus in consequence of a marriage contract, and received in return five hundred elephants.
but since the extensive sources available on Seleucus never mention an Indian princess, it is thought that the marital alliance went the other way, with Chandragupta himself or his son Bindusara marrying a Seleucid princess, in accordance with contemporary Greek practices to form dynastic alliances. From him, Vindusara was born and ruled for the same number of years as his father.
The Mudrarakshasa of Visakhadutta as well as the Jaina work Parisishtaparvan talk of Chandragupta's alliance with the Himalayan king Parvatka, often identified with Porus, and according to these accounts, this alliance gave Chandragupta a composite and powerful army made up of Yavanas (Greeks), Kambojas, Shakas (Scythians), Kiratas (Nepalese), Parasikas (Persians) and Bahlikas (Bactrians) who took Pataliputra.
In 305 BC, Seleucus I led an army to the Indus, where he encountered Chandragupta.
The most famous Indo-Greek ruler was Menander (Milinda).
Overland trade continued at a reduced rate, while sea trade between Greek Egypt and Bactria developed.
Diodotus was succeeded by his son Diodotus II, who allied himself with the Parthian Arsaces in his fight against Seleucus II: Soon after, relieved by the death of Diodotus, Arsaces made peace and concluded an alliance with his son, also by the name of Diodotus; some time later he fought against Seleucos who came to punish the rebels, and he prevailed: the Parthians celebrated this day as the one that marked the beginning of their freedom and possibly satrap of Sogdiana, overthrew Diodotus II around 230 BC and started his own dynasty.
He had his capital at Sakala in the Punjab (present-day Sialkot, Punjab, Pakistan).
The expression "Indo-Greek Kingdom" loosely describes a number of various dynastic polities, traditionally associated with a number of regional capitals like Taxila, Other potential centers are only hinted at; for instance, Ptolemy's Geographia and the nomenclature of later kings suggest that a certain Theophila in the south of the Indo-Greek sphere of influence may also have been a satrapal or royal seat at one time.
The Indian satrapies of the Punjab were left to the rule of Porus and Taxiles, who were confirmed again at the Treaty of Triparadisus in 321 BC, and remaining Greek troops in these satrapies were left under the command of general Eudemus.