The British formally annexed Manipur following their victory in the:

Anglo-Manipuri War (1891)
First Anglo-Burmese War
Battle of Khongjom
Seven Years' Devastation

The correct answer is: a) Anglo-Manipuri War (1891).

The Anglo-Manipuri War was a war fought between the British Empire and the Kingdom of Manipur from 24 March to 27 April 1891. The war was caused by a dispute over the succession to the Manipuri throne. The British supported the claim of Chura Chand, while the Manipuris supported the claim of Tikendrajit Singh. The war ended with the defeat of the Manipuris and the annexation of Manipur by the British.

The First Anglo-Burmese War was a war fought between the British East India Company and the Kingdom of Burma from 1824 to 1826. The war was caused by a dispute over the border between British India and Burma. The war ended with the defeat of Burma and the signing of the Treaty of Yandabo, which ceded Assam, Manipur, and Cachar to the British.

The Battle of Khongjom was a battle fought between the British and the Manipuris on 23 April 1891. The battle was part of the Anglo-Manipuri War. The battle ended with the defeat of the Manipuris and the death of Tikendrajit Singh.

The Seven Years’ Devastation was a period of famine and disease that struck Manipur from 1759 to 1766. The famine was caused by a combination of factors, including drought, crop failure, and war. The famine resulted in the deaths of an estimated one-third of the Manipuri population.