On May 10, 1857, the XI Native Cavalry of the Bengal Army, based in Meerut, mutinied against their British commanders. This was the beginning of many mutinies and rebellions around India, centered in Northern and Central India.
Reasons behind the rebellion:
Within the Army
The original soldiers in the Bengal Army had been mainly from the Brahmin and Rajput castes, but increasingly, the British were recruiting lower caste soldiers, thus angering the Brahmins and Rajputs because this reduced their social status. In addition, after the British had conquered Awadh and the Punjab, the soldiers no longer received extra pay for missions there, because they were no longer considered "foreign missions".
The tipping point was over Lee Enfield rifles. It was rumored that the cartridges for these rifles were greased with cow and pig fat, offensive to both Muslims and Hindus. Some soldiers refused to fire these rifles; they were either dismissed or imprisoned. Eventually, having seen enough, the rest of the soldiers mutinied.
Many members of the aristocracy deplored the British untrustworthiness. Treaties were signed and forgotten when convenient and the Doctrine of Lapse was a transparent power grab. For example, Rani Lakshmi Bai, the female leader of Jhansi which had been claimed in 1853 by the British, led a strong rebellion.
There was a distinctly Muslim character to some of the rebellions. There were calls for jihad by some leaders, including the millenarian Ahmedullah Shah. However, this led to some sectarian disagreements. For example, in Awadh, Sunni Muslims didn't want to see a return to Shiite rule, so they often refused to join what they perceived to be a Shia rebellion. In addition, a conscious effort was made to de-stress some of the religious elements in order to get support from Hindus. However, it is true that many people, particular Muslim artisans, fought for religious reasons.
There were different kinds of agrarian revolts...