Sikhism was started in 1519 by Guru Nanak (1469–1538) in Punjab. He was born a Hindu but reared in the democratic doctrine of Islam. He rejected the caste system of Hinduism and founded his faith as a doctrine of loving devotion to “one God, the Creator” whose name was Truth (Sat). He spoke of his belief in one deity, discounting the lesser gods and goddesses of Hinduism. The deity of Sikhism was not a human figure; rather, it was an overarching idea that encompassed the infinite reaches of the universe. Nanak taught that meditation and repetition of the deity's name was essential to becoming one with the deity. Sikhism shared with Hinduism its belief that the soul was stuck in a cycle of birth and rebirth until its eventual enlightenment allowed it to become free.

Nanak rejected all of the impurities of Hinduism, speaking out against the caste system and Hindu practices such as female infanticide and the burning of widows. He believed that one's destiny was predetermined. One was fated to perform certain actions, good or bad, and there was no way to change one's place in the cycle of birth and rebirth. Nanak decried both the elaborate ceremonies and extreme asceticism of Hinduism. Instead, he preached that people could find salvation by embracing unselfish ways and following an enlightened guru. His message was especially appealing to the lower castes, who seized upon the idea that all people should be equal in society.