The following factors were responsible for the outbreak of the Kalinga war in 261 B.C.
The Magadhan Empire during Asoka had surrounded Kalinga in the north, west and south. Tile existence of Kalinga as a powerful neighbour on the border of Magadha was definitely a threat to the power and potentiality of the latter. Thus, Kalinga posed a menace to the grand Magadhan empire. Before Kalinga rose to that extent, Asoka wanted to defeat and capture it.
Imperialistic design of Ashoka
Asoka’s invasion of Kalinga in 261 B.C. appears to have been actuated by his imperialistic designs. By the time of Asoka’s accession the Magadhan Empire had spread over most parts of India. From the Himalayas in the north to Mysore in the sourth and from the Kabul valley in the north-west to Bengal in the east, the whole territory was under the sovereignty of Ashoka. An independent kingdom of Kalinga, not very far from the centre of gravity of the Magadhan empire, was intolerable for a warlike- king like Chandasoka or Black Asoka .
Economic prosperity of Kalinga
There were certain economic factors which had created rivalry between Kalinga and Magadha. Kalinga monopolised the oversea trade in the Indian ocean and gained vast wealth. Her wealth also increased from inland trade. Through the Mauryas had foreign relation with the contemporary Hellenistic powers, they had not maintained commercial relation with them. It may also be pointed out that the Mauryas by that time had not built up a naval power and the Navadhyaksha (Superintendent of Shiping) mentioned by Kautilya in his Arthasastra was in charge of policing the rivers, lakes and seashores rather than building ships for maritime trades. So, the economic prosperity of Kalinga became an eye-sore for Magadha.
In trade and commerce, Kalinga was a great competitor of Magadha. Important trade-routes from the Gangetic valley to the Deccan and further south passed through Kalinga facilitating her trade and commerce. Though, Magadha had foreign relation and huge internal resources, it suffered from a commercial crisis due to the lack of trade routes. The existence of flourishing Kalinga with her trade and commerce was adversely affecting the economy of the Mauryan empire.
Stealing of Asoka’s jewels by the Nagas
According to the description of Lama Taranath, a Tibetan author, the Nagas stole away the jewels of Asoka. So, the emperor became angry and conquered their territory. These Nagas were identified with the seafaring people of Kalinga. In order to take revenge, Asoka invaded Kalinga.
Legend of Karuvaki
A strange story regarding the cause of Kalinga war prevails among the fisherman community of the eastern coast of Odisha. According to this, Asoka invaded Kalinga being infatuated by the beauty of Karuvaki, the daughter of a fisherman and the fiancee of the crown prince of Kalinga. Though this fact appears absurd, but it cannot be rejected outright because from the Queen’s Edict, it is known that Asoka had a queen named Karuvaki who was the mother of Tivara, a son of Ashoka.
Religion was another potential factor for Asoka’s invasion of Kalinga. Before Kalinga War, Asoka was a devout Saiva. Though, it is difficult to ascertain what was the prevalent form of religion in Kalinga, with tolerable degree of certainty, it can be stated that Buddhism and not Brahminism (Saivism) was prevailing in Kalinga. Asoka might have decided to wage a holy war against Kalinga to teach the Buddhists a lesson. Though, nothing concrete is available to the historians regarding the nature of polity in Kalinga during Asoka’s invasion· and also the state of religion in this land, it appears that Brahmanism, as a state religion, did not prevail here. However, this is a controversial issue.