Impact of Jainism and Buddhism.
Buddhism and Jainism arose as reactions to the Brahmanism about half a millennium before christ and had a great cathartic effect. Aiming primarily to remove the ills of Brahmanical Hinduism, they ended up being distinct religions in their own right. The Indians of 6th and 5th century BCE had become oppressed by the elaborate rituals and monopoly of Brahmins in religious matters. Hence the onset of both these religions had profound influences on society, polity, ideology etc of India.
In course of time, Jainism was only limited to Rajasthan and Gujrat, while Buddhism vanished from India and flourished in Sri Lanka, SE Asia, China and Japan.
Impact of Islam.
The word islam has been derived from a root word which means "surrendering oneself to God". When Muhammed preached the doctrine of one God in polytheistic Arabia, he was suggesting a great social change. One God meant the concept of social equality. Muslim rule began in India in the 13th Century AD with the establishment of Slave Dynasty.