The Vaishnava Bhakti movement originated in South India between the 12th-15th century AD as a response to degradation in Hindu society. It advocated devotion to Vishnu as a simpler, more inclusive faith that could provide salvation to all castes. The movement spread across India through figures like the Alvars and emphasized bhakti, or devotion, particularly through worship of Vishnu and his avatars. It initiated social reforms by challenging the caste system and established the centrality of bhakti in Hindu religious life.