Explanation:

The First Anglo-Burmese War commenced in 1824, and by March 28 the British had occupied Guwahati, when the Raja of Darrang submitted themselves to the British, who made rudimentary administrative arrangements by October 1824. The Burmese occupiers retreated from the Ahom capital of Rangpur in January 1825 and the nearly the whole of Brahmaputra Valley fell into British hands. In 1828, the Kachari kingdom was annexed under the Doctrine of Lapse after the king Govinda Chandra was killed. In 1832, the Khasi king surrendered and the British increased their influence over the Jaintia ruler. In 1833, upper Assam became a British protectorate under the erstwhile ruler of the Ahom kingdom, Purandhar Singha, but in 1838 the region was formally annexed into the British empire.