Bhagvatism, contemporary to Buddhism and Jainism in origin, owed its birth to the ideas in Upanishad.
Gupta rulers provided patronage to Bhagavata Sect of Hinduism. They called themselves Bhagavatas, worshipped Lord Vishnu, performed Ashvamedha yajnas, gave large donations to brahmanas, and built many temples. Puranas were compiled in this age.
Vishnu emerged as the god of devotion and came to be represented as the preserver of dharma. Numerous legends gathered around him and a whole Purana called Vishnu Purana was compiled in his honour. A law book called the Vishnusmriti was named after him.
By the 4th century AD, there came into being a famous Vaishnava work called ‘Shrimadbhagavad-purana’ which taught devotion to Lord Krishna.