The British had imperialized India long before 1857 and had sphere of influence. The sepoys were Indians in the British army.
The sepoys had gotten mad and started to disobey the British. This is because the rifle cartridges were greased with pig fat and beef tallow. Eating beef was against the Hindus religion and eating pig was against the Muslim religion.
The Sepoys will not follow what the British are saying because it is against their religion even though the British is saying they will kill them. It was like the Sepoys were missionaries. like this the Indians were treated very unfairly. The British were like the Elite and always ordered the Indians on what to do.
The Sepoys did not want to listen to the British because what they were saying to do went against the Sepoy religion. Therefore this resulted in Sepoy Rebellion(war).
The rule of the East India company was destroyed in result of the war. It was also entertained that certain reforms gave greater voice to Indians and government.
In conclusion the British had won the war and the british crown assumed direct control of the colony. Thank god the British didn't think of genocide or else India would have been a different place.