By the year 1857, the British East India company was in control of large parts of the country of India. They were able to tax, raise armies, and take over some regions of the country (The Sepoy Rebellion). They didn't respect the rights of the Indian citizens that they were leading, and some of them started to grow tired of it. The widespread unrest of the soldiers and citizens eventually grew into a mutiny in 1857 known as the Sepoy Mutiny, and although it was defeated by the British, it set the tone for more Indian independence movements (India Netzone). Along with many others, the primary causes that pushed the Indians and sepoys, Indian soldiers working for the British East India Company, over the edge and caused the Sepoy Mutiny were religious, political, and economic.
The British East India Company didn't respect the religious rights of the Hindus and Muslims who were members of the company's army or the other Indian citizens. The major threat perceived by the Indian people was the threat to the native religions of India (The Indian Mutiny). The British East India Company had only been interested in trade and business when they first got to India, but by the 19th century they were starting to take more interest in religious matters (The Indian Mutiny). East India personnel began to allow Christian missionary work to be carried out, and British officers started to expose their Indian soldiers to Christian teachings. This, along with the spread of western technology such as the telegraph and railways, had the people believing that the English were trying to convert them all to Christianity and get rid of their native religions (India Netzone).
Another religious reason was the newly introduced Enfield rifle. The soldiers needed to bite off the tip of the cartridge in order to load it properly. To keep the cartridges safe from the elements, they had been coated in grease made from the fat of pigs and cows.