What was the main reason behind the sepoy rebellion of 1857?

The Sepoy Rebellion of 1857 was an uprising against the colonial rulers in British India. It was the largest uprising of the 19th century against a colonial ruler, anywhere in the world. The rebellion began with a mutiny of sepoys, Indian soldiers employed by the British, in Bengal. From that area the rebellion spread over Hindustan. It became a serious threat to the British when Indian princes such as the nawab of Awadh and the Mogul emperor in Delhi chose the side of the mutiny.  

The sepoys were Indian auxiliary troops deployed by the British colonial administration. They included both Hindus and Muslims. In 1857 their number was of 190,000 men, who were paid by the East India Company.  

There was general dissatisfaction with the way the English treated the Indian princes and with the exploitation of the impoverished farmers. The uprising broke out as a result of the discovery that rifle bullets were smeared with pork or beef fat, causing both Hindus and Muslims to be hurt in their religious feelings. The rebellion was initiated by Mangal Pandey and the main captain was Nana Sahib.

However, the uprising failed because most of the princes remained loyal to the British administration and other indigenous troops such as the Sikhs and Gurkhas did not join. The uprising lasted until the beginning of 1858 and was eventually suppressed by the English with barbaric punishment. It led to the collapse of the British East India Company and to placing British India under the English crown. The Sepoy regiments were then reorganized.

a goverment for the people by the people

someone or something lol