The British annexation of which region played a major role in triggering the…

British annexation policies before 1857 - including the Doctrine of Lapse and annexations on grounds of alleged misgovernance - dispossessed rulers and disrupted the economic and social position of the people, including sepoys, tied to those states. This generated widespread resentment that fed directly into the causes of the Revolt of 1857.

The Company annexed Oudh (Awadh) in 1856 under Governor-General Lord Dalhousie, citing misgovernance by the Nawab, despite the state's long-standing alliance with the British. A very large proportion of the sepoys of the Bengal Army were recruited from Oudh; the annexation stripped local taluqdars of their land-revenue rights and left sepoys' families economically and socially unsettled. This resentment, compounding with other grievances such as the greased-cartridges controversy, made Oudh a central flashpoint, and its annexation is identified by historians as a leading cause of the Sepoy Mutiny of 1857.

Why the other regions do not fit:

• Bengal: the seat of Company administration since 1757 (after the Battle of Plassey) - long-established British territory, not a newly annexed area whose annexation itself triggered unrest in 1857.

• Mysore: came under British control after the Anglo-Mysore Wars, concluding in 1799 with the defeat of Tipu Sultan - decades before 1857, unconnected to the immediate causes of the revolt.

• Delhi: the symbolic seat of Mughal authority and a rallying centre for rebels once the uprising began, but not the region whose annexation is credited with precipitating the mutiny.

Hence, the annexation of Oudh (Awadh) is the event that matches the historical cause of the Sepoy Mutiny of 1857.