Historians have identified diverse political, economic, military, religious and social causes of the Indian Rebellion of 1857 (First War of Indian Independence).
An uprising in several sepoy companies of the Bengal army was sparked by the issue of new gunpowder cartridges for the Enfield rifle in February 1857. Loading the Enfield often required tearing open the greased cartridge with one's teeth, and many sepoys believed that the cartridges were greased with cow and pig fat. That would have insulted both Hindu and Muslim religious practices; cows were considered holy by Hindus, and pigs were considered unclean (Haram) by Muslims.
Underlying grievances over British taxation and recent land annexations by the East India Company (EIC) also contributed to the anger of the sepoy mutineers, and within weeks, dozens of units of the Indian army joined peasant armies in widespread rebellion. The old aristocracy, both Muslim and Hindu, who were seeing their power steadily eroded by the EIC, also rebelled against British rule.
Another important source of discontent among the Indian rulers was that the British policies of conquest had created significant unrest. In the decade prior to the rebellion, the EIC had imposed a "doctrine of lapse" of Indian leadership succession and the policy of "subsidiary alliance", both of which deprived many Indian rulers of their customary powers and privileges.
Frictions
Some Indians were upset with the draconian rule of the Company who had embarked on a project of territorial expansion and westernization that was imposed without any regard for historical subtleties in Indian society. Furthermore, legal changes introduced by the British were accompanied by prohibitions on Indian religious customs and were seen as steps towards forced conversion to Christianity. As early as the Charter Act of 1813 Christian missionaries were encouraged to come to Bombay and Calcutta under EIC control. The British Governor-General of India from 1848 to 1856 was Lord Dalhousie, who passed the Widow Remarriage Act of 1856, which allowed widows to remarry, like Christian women. He also passed decrees allowing Hindus who had converted to Christianity to be able to inherit property, which had been denied by local practice.
Thwe author Pramod Nayar points out that by 1851 there were nineteen Protestant religious societies operating in India, and their goal was the conversion of Indians to Christianity. Christian organisations from Britain had additionally created 222 "unattached" mission stations across India in the decade preceding the rebellion.
Religious disquiet as the cause of rebellion underlies the work of the historian William Dalrymple, who asserts that the rebels were motivated primarily by resistance to the actions of the East India Company, especially under James Broun-Ramsay reign, which were perceived as attempts to impose Christianity and Christian laws in India. For instance, once the rebellion was underway, Mughal Emperor Bahadur Shah Zafar met the sepoys on 11 May 1857, he was told: "We have joined hands to protect our religion and our faith." They later stood in Chandni Chowk, the main square, and asked the people gathered there, "Brothers, are you with those of the faith?" Those European men and women who had converted to Islam such as Sergeant-Major Gordon, and Abdullah Beg, a former Company soldier, were spared. In contrast, foreign Christians such as Revd Midgeley, John Jennings, and Indian converts to Christianity such as one of Zafar's personal physicians, Dr. Chaman Lal, were killed.
Dalrymple further points out that as late as 6 September, when calling the inhabitants of Delhi to rally against the upcoming Company assault, Zafar issued a proclamation stating that this was a religious war being prosecuted on behalf of 'the faith', and that all Muslim and Hindu residents of the imperial city, or of the countryside were encouraged to stay true to their faith and creeds. As further evidence, he observes that the Urdu sources of the pre rebellion and post-rebellion periods usually refer to the British not as angrez (the English), goras (whites) or firangis (foreigners) but as kafir (disbeliever) and nasrani (Christians).
Some historians have suggested that the impact of British economic and social reforms has been greatly exaggerated, since the Company did not have the resources to enforce them, meaning that away from Calcutta their effect was negligible.