The kingdom of Kosala covered the territories of Oudh and was ruled by king Mahakosala and his more powerful son Prasenajit who was a contemporary of Buddha. King Prasenajit was known for his devotion to Buddha, without being a Buddhist. His respect for Jaina and Brahminical faiths was also deep.
Location: In their ambition, the kings of Kosala conquered lands far and wide. It roughly corresponded to modern Oudh. Its chief towns were, Ayodhya, Saketa and Saraswati, the last two were then counted among the six great cities of India.
Origin: These rulers claimed themselves as the descendants of the mythical monarch Ikshvaku.
Powerful: The Buddha’s contemporary ruler of Kosala was King Prasenajit, who is counted as one of the most important rulers of his time. He had inherited a state which had already become very powerful because of the absorption of Kasi in its territories.
Admirer of Buddhism: King Prasenajit was a highly educated man who had received his education at the celebrated seat of learning, i.e. Taxila. Although not actually converted to Buddhism, he was favorably inclined towards this movement. He was a great friend and an admirer of Buddha. One of the Bharhut sculptures commemorates the relation between Prasenajit and Buddha.
Relation with Magadha: Moreover Prasenajit’s position had become still more important because of his sister’s marriage with Bimbisara, the king of Magadha. Later on this marriage however, led to a war between Kosala and Magadha. The war broke out when Ajatasatru, Bimbisara’s son by another wife (from Mithila), put his father to death and Kosala Devi, Prasenajit’s sister, died of grief. The war continued for some time with varying fortunes. It ended, however, in a happy reconciliation between Ajatasatru and Prasenajit, the latter marrying his daughter Vajjira to the former and giving the township of Kasi in dispute as a gift to her daughter.
Last Days of Prasenajit: The last days of Prasenajit were, however, not very happy. When the king had gone to the Sakya country to meet Buddha his own son Virudaka (or Vidudabha) revolted against him and he had to rush to Rajagriha for help. But he was not destined to reach there. Because of fatigue and worry he died outside the gates of that city. Ajatasatru gave a state funeral to his father-in law.
Successors of Prasenajit: After Prasenajit, Vidudabha came to the throne of Kosala attacked the Sakya territory because he felt that they had instigated his father against him and in retaliation he killed a large number of the Sakyas. This happened a year or two before Buddha’s death, But soon dissensions broke out in Kosala and we hear very little of this empire.
Annexed to Magadha Empire: Later-on, with course of time, Kosala Kingdom itself became a victim to the growing power of Magadha. It became part of Magadha Kingdom.