India had to face foreign invasions, apart from massive migrations, several times across centuries. The earliest of these in history was the invasion by the Ackaemenid Empire of Persian 6th and 5th century BC. Now enters the well-organized army of Alexander of Macedon towards the close of 4th century BC. He conquered several kingdoms of the North-West of India, and proceeded towards the East. But he had to return to Macedon because of certain internal problems which cropped up there. Though he vanished from the Indian scene, the impact his invasion of India cast an enduring influence in the cultural life the country for centuries. The Greek culture that Alexander brought to India paved the way for what is called Greco-Buddhism and this spread to far away countries too, like Japan, Korea, China and the countries of Central Asia.

This area was not of a single tribe or a single language and culture. It was inhabited by people of various tribal clans and of several languages of diverse language families. Kamboj was one among the various states, and Gandhara another.  Towards the close of the 6th century B.C., some areas of the North-Western India were annexed to the Ackaemenid empire. Darius (522-486 B.C.), the famous emperor of Ackaemenid, declared Gandhara and the surrounding areas part of his empire and this was inscribed in a rock edict. Though only a part of the North-West India was annexed by Darius, even other parts of the North-West India was greatly influenced by the cultural and other influences of the Achaemenid Persia.  Though Persians knew of this part of India, they knew very little about the eastern India.