India in the nineteenth century
The East India Company was a company with an empire. It had its own army, with British officers and Indian 'sepoy' soldiers. And by 1850, it controlled most of India. Even the parts that still had rajahs and nawabs were 'protected' by Britain.
The British thought that they had brought law and order and progress to India. So they were appalled in May 1857 when the sepoy soldiers revolted and took Delhi and other towns in the north. But the British fought back, and within a year they were in control again. Both sides were guilty of many savage crimes.
The British called it a 'mutiny'. They said that the main cause was that the sepoys did not like the new greased cartridges which they had to use. (This was to do with religion. Hindu soldiers said that the grease was beef fat, and cows are sacred to Hindus. Muslims thought that it was pork fat, and Muslims are not allowed to eat pork.)
Indians called it a rebellion against foreign rule. They had a long list of complaints. The British had taken away the lands of the rajahs and nawabs. No Indians were employed as judges, army officers, or in other senior jobs. The British did not respect Indian customs and laws. And imports of British cotton cloth had damaged Indian trade.
The rebellion (or mutiny) failed. But the British learned lessons from it. They ended the rule of the East India Company. In future, a viceroy ruled India in the name of the queen. They went on using Indian troops, but the number of British soldiers in India was greatly increased.
Walter Robson: Britain 1750 – 1900; Oxford University Press, 1993/2002, page 74 f.