The Cambridge History of India, Vol. I: Ancient India v1.c19.s3.9

v1.c19.s3.9

No references have so far been found in the books as to any contests between Kosala and any other tribe or nationality. It would seem therefore that the gradual absorption into Kosala of the clans and tribes in the northern part of Kosala as we know it in the Buddha's time took place without any such battle, campaign, or siege as was sufficiently striking to impress the popular imagination; but that when Kosala came into contact with Kāsi there ensued a struggle, with varying result and lasting through several reigns, which ended in the complete subjugation of the Kāsi country by Kaṁsa, king of Kosala.