The Bengal army, recruited heavily from high-caste Brahmins, Rajputs and Muslims of Awadh and Bihar, was the powerhouse of the Company's military strength — and its deepest grievance. Sepoys received low pay, poor promotions, were barred from the highest ranks, and feared the General Service Enlistment Act (1856), which required them to serve overseas and thereby lose caste.

Rumours that the new Enfield rifle cartridges were greased with cow and pig fat broke the sepoys' last trust. When 85 sepoys of the Meerut garrison were court-martialled and imprisoned on 9 May 1857 for refusing the cartridges, their comrades rose the next day and marched on Delhi, beginning the revolt.