Things such as abolition of sati, legalisation of widow remarriage and introduction of women education system made orthodox Hindus uncomfortable and made them feel as if their beliefs were being attacked.
Lands belonging to temples and mosques were taxed
Political Causes
British Policies such as Doctrine of Lapse turned kings and princes into mere subordinates
Expansionist policies of the British made the Indian rulers suspicious of the British's intentions.
Immediate Cause
In 1856, the enfield rifle was introduced in the the army and their cartridges which have to be bitten off are smeared with grease which is made from animal fat, however this went against Hindus religious beliefs. Mangal Pandey, of the 34th Infantry Division at Barrackpore refused to use them on March 29th 1857. He was arrested and hanged on 8th April, 1857.
Military Causes
Indian Sepoys were considered inferior and payed lesser than their European counter parts
Promotions of Indians were very limited and they could not rise beyond the rank of subedar
Economic Causes
The British confiscated land of old zamindars, especially in Awadh
Artisans and craftsmen were ruined because of large-scale import of cheap British manufactured goods.