Explanation:

Cooch Behar State was formed when the Kamata Kingdom under the Koch dynasty split following the death of Nara Narayan in 1586. The eastern portion, Koch Hajo, was soon absorbed by Ahom. The western portion, Koch Bihar, formed a separate unit that came under direct challenge by the Mughal Empire. After weathering the Mughal threat, a new foe emerged in the form of an expansionist Bhutanese kingdom. After a series of wars with the Bhutanese and Tibetans, the Northern threat was pushed back but not before a Bhutanese regent was installed in the royal court. The Koch Bihar court decided to invite British intervention. This came in the form of military assistance that—acting in concert with Koch Bihar forces—ended the Northern challenge once and for all. However the British East India company sought guarantees whereby the independence of Koch Bihar was limited by treaties. When the British colonial rule was finally terminated in India, the Koch Bihar state immediately acceded to and merged with India in 1950 and became a part of West Bengal. The district, Cooch Behar District, is named after this erstwhile kingdom.