In the spring of 1857 a number of units of the Bengal Army, one of three native armies in the employ of the East India Company, rebelled against British rule.
The reasons were complex, but one event that set things off was the introduction of a new rifle cartridge rumored to contain grease derived from pigs and cows. Such animal products were forbidden to Muslims and Hindus.
While the rifle cartridges may have been the final straw, relations between the East India Company and the native population had been degenerating for some time. And when the rebellion broke out, it became extremely violent.
This illustration depicts a charge a British Army unit made against gun batteries manned by mutinous India troops.