When the popularity of the bhakti movement in south India reached its peak, the doctrine of bhakti was expounded at the philosophical level by a series of Vaishnava scholars and saints. Ramanujar expounded the philosophy known as Vishistadvaita, or qualified monism. His teaching qualified Adi Sankara’s emphasis on absolute monism or the oneness of the ‘supreme’ and the ‘souls’. If the Bhakti movement flourished in the Tamil country from the seventh century, it was only from the fifteenth century that there was an extraordinary outburst of devotional poetry in north India. The society had degenerated into a caste-ridden community with practice of segregation, polytheism and idolatry. The religious minded saints raised their voice of protest against rites and ceremonies, superstitions, and unwanted formalisms. A popular monotheistic movement along with Vaishnava Bhakti movement came to be launched. The monotheists followed a path which was independent of dominant religions of the time, Hinduism and Islam. They denied their allegiance to either of them and criticized superstitious and orthodox elements of both the religions. The advent of Islam with the Turkish conquest posed a challenge to Vedic scholars and priests. By the end of the fourteenth century Islam had spread to large parts of India. A considerable section of the Indian population had taken to Islam. Combined with state power, the universal message of Islam with emphasis on equality attracted the lower sections of society. The new political and social situation created conditions for the growth of non-conformist movements with anti-caste, anti-vedic and antipuranic traditions. The resultant changes in the cultural sphere were: development of regional languages, the evolution of Hindustani, and of Indo-Muslim music and architecture. The Hindu response to Muslim political power was complex. While there was considerable hostility to the new religion there was also a tendency to internal reform to strengthen Hinduism so as to face the challenge. An important outcome of the encounter was the rise of syncretic sects and major poets and Saints such as Kabir, Guru Nanak, and Ravidas.