From the time of Alexander’s invasion, the lands outside the north-west frontiers of India became a political playground of the Greek powers.
The Mauyra emperors by their military power, kept them away from the Indian frontiers while ruling over territories outside the natural boundaries of geographical India.
After the fall of the Mauryas, the Greeks once again became active to invade India. But their own power began to decline in course of time.
For about two hundred years before the birth of Christ, the Central Asian lands saw extensive movements of different races of people. These races destroyed the Greek supremacy in those regions. Side by side they became a new source of danger to the north-west of India.
Among those people, three races were prominent. They were the Sakas, the Pahlavas or Parthians, and the Yueh-chi or Kushanas. Of them the Sakes were the most famous and the other races at times were described as the Sakas in general terms.
When the Indo-Greeks disappeared from the north-western India, these new comers looked upon those regions for occupation. They were nomadic homeless people in search of new homes. Some of them had been driven out from their original lands by more powerful tribes. They were also fighting among themselves for territorial gains and political powers. It was in that kind of racial migration and contest for lands that the Kushanas rose to power in Central Asia.
The origin of the Kushanas is known from the Chinese sources. In second century B.C., there lived in Western China a vast nomadic tribe named as the Yueh-chi. They were driven out from that place by another powerful tribe famous as the Hiung-nu or Hunas. When the Yueh-chi tribe entered into Central Asia they found there another powerful nomadic tribe known as the Sakas. Driven out by the Yueh-chi, the Sakas moved towards the frontiers of India.
In course of time, the Sakas entered into the Indian mainland and established themselves in Kashmir, the Punjab and on either side of the river Indus. But, in course of time, they began to lose their separate identity and got lost in the Indian population. They accepted Indian religions and became rapidly Indianised.
The Yueh-chi tribe, in the meantime, got settled in the Oxus valley in Bactria. Nomadic people as they were, at their new home, they quickly got divided into five branches. The- Kushanas were the most famous of those five groups. They, in their turn, aimed for more power and searched for more lands. Gradually the Kushanas entered into India, and ultimately formed a powerful state in the north-west. Though they dominated the Central Asian territories mostly, their power began to grow over a large part of India. Finally, a Kushana empire came into existence in India in due course.