This paper proposes to discover how the trade routes in Central Asia contributed to the development of the Kushan state and what role the five yabghus played in constituting the realm. A commonly accepted model places the ancestors of the Kushans into "northern Bactria", that is, the land north of the Oxus and south of the Serafshan range, between the Iron Gate west and the Pamir east. This land measures hardly 200 by 300 km. The standard model regards the Yuezhi, that is, the Kushans avant la lettre, as nomads rearing animals and shifting with the seasons down to the Oxus and north up to the Sogdian mountains. The expansion masterminded by the self-declared tyrant and first "Kushan" named Kujula Kadphises in around A.D. 30 made him and his immediate successors masters of northern India in less than 70 years. But how could a tribe of nomads could afford to finance war with mighty opponents in the west and south in northern India over such a long time and over such extended regions? The answer put forward is that the five local governors titled yabghu, through many decades prior to Kujula, regulated trade routes from the western end of Xinjiang up to the western regions of Bactra and down the Hindu Kush ranges, that is, an area extending over 800 km lengthwise, safeguarding trade on most of the caravan routes leaving China towards the west and south. That means that the eastern end of the Yuezhi realm in the last century B.C. was not near Dushanbe in northern Bactria, but rather in Tashkurgan at the eastern border of the Pamir plateau.