In the sixth century bc, the small republics were being conquered and merged with the main principalities and Magadha was emerging as a strong kingdom in the north-east. In the north-west, however, no one kingdom was more powerful than the rest and the small principalities like Kamboja and Gandhara fought for prominence.
This political turmoil must have encouraged the Persian invaders. The founder of the Achaemenian empire of Persia, Cyrus (558-530 bc) is said to have destroyed the city of Kapisa (near the junction of Ghorband and Panjshir rivers north-east of Kabul).
Darius (522-486 bc), invaded the north-west of India, annexed the Indus valley as far as the Rajasthan deserts and made this the 20th satrapy of the Persian empire out of a total of 28.
The fertile area was regarded as the most populous satrapy and its inhabitants paid a large tribute. The inscriptions of his ion and successor Xerexes refer to Daiva-worshipping lands which may have included the parts of north-west India as well.
Though regions north-west of India and the parts of the country adjacent to it continued under the Persian rule till Alexander’s invasion, small states practically independent kings seem to have emerged towards mid-fourth century bc. Some of the kingdoms and their rulers were:
(i) Area north of River Kabul drained by Swat and Kunar rivers under Asvakas (city of Nysa said to have been founded by Greek colonists was in this region).
(ii) The kingdom of Pushkalavati (in Peshawar district) to the west of River Indus,
(iii) Takshasila or Taxila (district of Rawalpindi) to the east of River Indus,
(iv) kingdom of Urasa (Hazara district) above the Taxila region,
(v) Abhisara kingdom just above the Taxila country,
(vi) Kingdom of the Purus or Pauravas to the south-east of Taxila,
(vii) Territory of the elder Poros (mentioned by Greek historians), between riversJhelum and Chenab, and
(viii) The territory of his nephew, between rivers Chenab and Ravi. The kingdoms in (ii) and (iii) constituted the earlier Gandhara territory.