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Northern India

The ancient emergence of Vaishnavism is unclear, the evidence inconsistent and scanty. Syncretism of various traditions resulted in Vaishnavism. Although Vishnu was a Vedic solar deity, he is mentioned less often compared to Agni, Indra, and other Vedic deities, thereby suggesting that he had a minor position in the Vedic religion.

According to Dandekar, what is understood today as Vaishnavism did not originate in Vedism at all, but emerged from the merger of several popular theistic traditions which developed after the decline of Brahmanism at the end of the Vedic period, closely before the second urbanisation of northern India, in the 7th to 4th century BCE. It initially formed as Vasudevism around Vāsudeva, a deified leader of the Vrishnis, and one of the Vrishni heroes. Later, Vāsudeva was amalgamated with Krishna "the deified tribal hero and religious leader of the Yadavas", to form the merged deity Bhagavan Vāsudeva-Krishna, due to the close relation between the tribes of the Vrishnis and the Yadavas. This was followed by a merger with the cult of Gopala-Krishna of the cowherd community of the Abhıras in the 4th century CE. The character of Gopala Krishna is often considered to be non-Vedic. According to Dandekar, such mergers consolidated the position of Krishnaism between the heterodox sramana movement and the orthodox Vedic religion. The "Greater Krsnaism", states Dandekar, then adopted the Rigvedic Vishnu as Supreme deity to increase its appeal towards orthodox elements.

According to Klostermaier, Vaishnavism originates in the latest centuries BCE and the early centuries CE, with the cult of the heroic Vāsudeva, a leading member of the Vrishni heroes, which was then amalgamated with Krishna, hero of the Yadavas, and still several centuries later with the "divine child" Bala Krishna of the Gopala traditions. According to Klostermaier, "In some books Krishna is presented as the founder and first teacher of the Bhagavata religion." According to Dalal, "The term Bhagavata seems to have developed from the concept of the Vedic deity Bhaga, and initially it seems to have been a monotheistic sect, independent of the Brahmanical pantheon."

The development of the Krishna-traditions was followed by a syncretism of these non-Vedic traditions with the Mahabharata canon, thus affiliating itself with Vedism in order to become acceptable to the orthodox establishment. The Vishnu of the Rig Veda was assimilated into non-Vedic Krishnaism and became the equivalent of the Supreme God. The appearance of Krishna as one of the Avatars of Vishnu dates to the period of the Sanskrit epics in the early centuries CE. The Bhagavad Gita —initially, a Krishnaite scripture, according to Friedhelm Hardy —was incorporated into the Mahabharata as a key text for Krishnaism.

Finally, the Narayana worshippers were also included, which further brahmanized Vaishnavism. The Nara-Narayana worshippers may have originated in Badari, a northern ridge of the Hindu Kush, and absorbed into the Vedic orthodoxy as Purusa Narayana. Purusa Narayana may have later been turned into Arjuna and Krsna.

In the late-Vedic texts (~1000 to 500 BCE), the concept of a metaphysical Brahman grows in prominence, and the Vaishnavism tradition considered Vishnu to be identical to Brahman, just like Shaivism and Shaktism consider Shiva and Devi to be Brahman respectively.

This complex history is reflected in the two main historical denominations of Vishnavism. The Bhagavats, worship Vāsudeva-Krishna, and are followers of Brahmanic Vaishnavism, while the Pacaratrins regard Narayana as their founder, and are followers of Tantric Vaishnavism.