Theravada group insisted understanding of ones self is the chief way to gain nirvana. through meditation and moral conduct.
Mahayana group believed the Theravada were too strict and believed that by devotion to Buddha, people can achieve salvation in this heaven.
Islam and Hindu: the Muslims tried to convert the Hindus to Islam but it didn't work. the Muslim rulers tried to maintain a strict separation between Muslim class and Hindu pop. Muslims accepted Hindu religion