The Kushanas are generally regarded as a branch of the nomadic Yue-chi tribe. During the first half of second century B.C., the Yue-Chis lived in the west of the Hwang-ho River in the provinces of Kang-su, Ning-hsia and Tun-Huang in China. These Yue-chi tribes were expelled from their original homeland of China by a vibrant nomadic Turkish tribe called Hiung-nu, after they killed the Yue chi chief. The Hiung-nu tribes were popularly known as the Huns. However the overthrow by the Huns led to a westward migration of the Yue-chi people.
The Yue-chis migrated westward under the guidance of the widow of their slain ruler and reached north of the Takla Makan desert. However the Yue-chi people had encountered several barriers during their migration to the west. At first, after reaching the region they came into conflict with the nomadic tribe Wu-sun, who were concentrated in the valley of the Ili River. The Wu-sun people were defeated and the Yue-chi tribes killed their ruler. The Yue-chis further marched west beyond the lake Issiq-Kul in search for their suitable homeland. At this point the Yue-chi people became divided into two groups. A small part detached themselves from the parent tribe and moved southward in order to settle in the Tibetan frontier. The main branch henceforth moved towards the west and met the Sakas populating the northern and southern banks of the river Syr Dariya. They ousted the Sakas from their original homeland, who were settled in the Kashmir region.
The Yue-chis were ousted from the Syr-Dariya valley by Kwen-Mo, son of the slain Wu San chief and the Yue-Chis allied with the Huns. Later the Yue chi tribes migrated further westward and settled in the Amu-Dariya valley by ousting the Sakas from that region. However there is a keen controversy regarding the fact about who had driven the Sakas out from the Amu-dariya river valley. Some historians have also opined that the Sakas were originally expelled from their homeland by the Bactrian Greeks and not by the Yue-Chis.
Sten Konow's explanation regarding Kushana Dynasty
There is a lot of controversy among the scholars regarding the origin and ancestry of the Kushanas, the most vibrant alien tribes in ancient India. Scholars hold different views about this fact based on their researches. According to a group of scholars, the Kushanas belonged to the Yue-Chi origin. The principal sources of information that the Kushanas belonged to the Yue-chi tribes are the two Chinese annals of the first and the later Han Dynasty. But Sten Konow explained that the Kushanas were not the descendants of the Yue-chi dynasty, rather he pointed towards the Saka kinship of the Kushanas. He has further pointed out that the language spoken by the Kushanas bore similarity with the Sakas. Language of the legends on the coins of the Imperial Kushanas was in pure Khotani Saka language. A keen research on the dress and weapons used by the Kushanas revealed the resemblance with the Sakas.
Maenchen-Hellen's theory regarding the Kushana Empire
The American scholar, Maenchen-Hellen however has provided a theory that provides solution to the entire controversy. According to Hellen, the Yue-chis had a branch named Kusha Yue-chi. They came under the Saka rule in an undetermined time and had blood mixture with them. Ultimately the Kusha Yue-Chis conquered the entire region of Bactria and by first century B.C. the Kusha Yue-Chis had great ascendancy over all other branches of the Yue Chi tribes.
Later Kusha Yue-chi came to be identified as the Kushanas. Kushanas did not possess purity of blood and they had a mixed origin. They absorbed the large Saka ethnic element among them. They seemed to have imbibed many cultural traits of the Sakas. The Kushanas therefore did not belong to any particular ancestry, they were of composite race.
Emergence of Kujala Kadhises in Kushana Empire
From the available historical records about the ancestry of the Kushanas, it is known that the Yue-Chis resided in Bactria and the Oxus valley was divided into five independent principalities. In the long run, Kujala Kadphises, Chief or Yabgou of the Kushana branch, defeated four other tribes, who themselves had independent princedoms. Kujala Kadphises, after victory assumed the title of a king. After that he united the four tribal branches under his supremacy. At the same time he also annexed the four principalities and consolidated his own Empire. In this way Kujala Kadphises not only asserted his full sovereignty, but also brought the other four branches of the Yue-chi under his empire.
After uniting the Yue Chis, Kujala Kadphises attacked Parthia, ruled by Arsakas. Then he set out to capture Kabul and annexed Pota (territory adjoining Kabul) and Ki-pin (Kafristan) under his realm. Later historians identified the Ki-pin or the Kafristan region as the Western border of India, including Kashmir. Dr. B.N Mukherjee has pointed out that the whole region from Parthia to Ki-pin belonged to the Arsakian dynasty, which was overthrown by the Kushana Chief Kujala Kadphises. According to Sten Konow, Kujala's conquest did not stop in India's borderland. The discovery of his coins in Taxila testifies his conquest of the territory. But Dr. Jagannath had refuted Konow's theory and pointed out that Kujala never penetrated beyond the Indian limits. According to several other historians, the Indo Greek king Hermaeus allied with Kadphises against his Parthian adversary. However historians held this view because the coins discovered had the name of the Indo-Greek king in the front side and the name of Kujala Kadphises on the reverse side in Kharosti. Hence, according to those historians, Kujala Kadphises was the subordinate king of the last Indo-Greek king Hermaeus. Later this view was absolutely discarded by Rapson. Rapson had suggested that a wide gap existed between the Indo-Greek king Hermaeus and the Kushana king Kujala Kadphises. It is now presumed that Kujala Kadphises inscribed his own name in the coins of Hermaeus in the region where the coins was still in use even after Hermaeus's death. In his coins Kujala Kadphises described himself as "Dharmasthita" and "Satyadhamasthita", which indicated his allegiance towards Buddhism. Kujala Kadphises died at the age of eighty and was succeeded by his son, Yen-kao-tchen. Yen-kao-tchen was identified with Wema Kadphises. According to the history of the Han Dynasty, Wema succeeded his father to the throne. Though his ascension is a disputed one, yet the general view is that he ascended his father's throne in 64 A.D. and reigned upto 78 A.D.