The Kalinga War of 261 B.C. is considered as the sheet anchor of Odishan history. With it begins the dated history of Orissa. The Mauryan influence over Kalinga not only added a new feather in the already crowned Magadhan imperialism, but it also brought about a radical change in the existing polity of the land. Though the Nandas had established their authority over Kalinga, they had probably altered the existing administrative set up of Kalinga. After Kalinga war , an elaborate system of administration was arranged by Ashoka for this newly conquered province.
A detailed account of this war is known from Rock Edict XIII found at Shahbazgarh in Pakistan. Kainga was under the suzerainty of Magadha till Dhana Nanda. Kalinga probably slipped away from the fold of Magadhan imperialism when Kautilya and Chandragupta Maurya revolted against the Nandas around 322-321 B.C. Chandragupta Maurya had never attempted to annex Kalinga during his life time. Bindusara had also not fought with the people of Kalinga. So, it was a historic necessity on the part of Asoka to conquer Kalinga.
The Kalinga war was a land mark in the history of ancient Odisha. It left some permanent legacies. The war gave to this land with its predominant aboriginal and primitive population a civilized administration which could achieve its moral and social uplift by its constant solicitude and work for the welfare of the people. Buddhism became a world religion after the war. Ashoka’s rule also resulted in the introduction of Mauryan art and architecture in Odisha.