The Greeks in Bactria and India c10.s5.24

c10.s5.24

Before coming to the details of that conquest one must just glance at the cause of the nomad invasion which swept away the Greek kingdom of Bactria and came near to overrunning Parthia also. It has been powerfully urged⁴ that most of the historical invasions of the settled lands of Asia by nomads from the Eurasian steppes, including the one to be described in this chapter, followed fixed laws and were due, in whole or in part, to a regular climatic period,⁵ an alternation of humidity and aridity which worked in 600-year cycles; the periodic increase in the fertility of the soil led to an increase in the nomadic population,¹ and the subsequent decrease of fertility and consequently of the food supply forced the hungry nomads, whose grazing grounds no longer sufficed them, to invade the settled lands. But in the case we have to consider, the movements of the various Saca peoples we shall meet (except the Massagetae) are fully accounted for by the disturbances due to the advent of the Yueh-chi. No doubt the sequel in India shows that the Saca world *was* over-populated, but had it been underpopulated the movements would have been the same; for the ultimate reason why the Sai-wang and the Sacaraucae—one may add the Yueh-chi themselves, for that matter—came south was that they were driven by superior force. The Massagetae alone appear to have been free agents; Bactria and Khorasan had attracted them from the time of Euthydemus (p. 117) and doubtless earlier, and what brought them south was not compulsion but opportunity, an opportunity which they did not mean to leave entirely to others.