Bhagavatism originated in post-Maurya times and centred around the worship of Vishnu or Bhagavata.
Vishnu was a minor god in Vedic times. He represented the sun and also the fertility cult. By the second century BC he was merged with a god called Narayana, and came to be known as Narayana-Vishnu.
Originally Narayana was a non-Vedic tribal god called bhagavata, and his worshippers were called bhagavatas. This god was conceived as a divine counterpart of the tribal chief.
Just as a tribal chief received presents from his kinsmen and distributed shares among them, Narayana also was supposed to bestow shares or good fortune (bhagya) on his bhakta or worshippers. In return the worshippers or bhaktas offered their loving devotion or bhakti to him. The worshippers of Vishnu and those of Narayana were brought under a single umbrella by merging Vishnu with Narayana. The former was a Vedic god and the latter emerged subsequently with non-Vedic associations, but the two cultures, the two types of peoples, and the two gods mingled and merged.
Besides, Vishnu came to be identified with a legendary hero of the Vrishni tribe living in western India who was known as Krishna-Vasudeva. The great epic Mahabharata was recast to show that Krishna and Vishnu were one. Thus, by 200 BC the three streams of gods and their worshippers merged into one and resulted in the creation of Bhagavatism or Vaishnavism.
Bhagavatism was marked by bhakti and ahimsa. Bhakti meant the offer of loving devotion. It was a kind of loyalty offered by a tribal to his chief or by a subject to his king. Ahimsa, or the doctrine of non-killing of animals, suited the agricultural society and was in keeping with the old cult of life- giving fertility associated with Vishnu. People worshipped the image of Vishnu, and offered it rice, sesamum, etc. Out of their aversion to killing animals, some of them took to an entirely vegetarian diet.
The new religion was sufficiently liberal to attract foreigners. It also appealed to artisans and merchants who became important under the Satavahanas and Kushans. Krishna taught in the Bhagavadgita that even women, vaishyas, and shudras who were born of sin could seek refuge in him.
This religious text dealt with the Vaishnava teachings, as did the Vishnu Purana, and also to an extent the Vishnu Smriti. Bhagavatism or Vaishnavism overshadowed Mahayana Buddhism by Gupta times. It preached the doctrine of incarnation, or avatar. History was presented as a cycle of the ten incarnations of Vishnu. It was believed that whenever the social order faced a crisis, Vishnu appeared in human form to save it.
Each incarnation of Vishnu was considered necessary for the salvation of dharma which coincided with the varna divided society and the institution of the patriarchal family protected by the state. By the sixth century Vishnu became a member of the trinity of gods along with Shiva and Brahma, but was a dominant god in his own right. After the sixth century, several texts were written to popularize the virtues of worshipping him, but the most important was the Bhagavata Purana. The story in that text was recited by priests for several days.
In medieval times bhagavatagharas or places meant for Vishnu worship and recitation of the legends associated with him began to be established in eastern India. Several religious recitations, including the Vishnusahasranama, were composed for the benefit of Vishnu worshippers. A few Gupta kings were worshippers of Shiva, the god of destruction, but he came to the fore at a later stage, and does not seem to have been as important as Vishnu in the early phase of the Gupta rule.
Idol worship in the temples became a common feature of Hinduism from the Gupta period onwards and many festivals also began to be celebrated. Agricultural festivals observed by different classes of people were lent a religious garb and colour, and turned into useful sources of income for the priests. The Gupta kings followed a policy of tolerance towards different religious sects. We find no example of the persecution of the followers of Buddhism and Jainism. This was also due to the change in the character of Buddhism which had come to acquire many features of Brahmanism or Hinduism.