India has been an important part of three major world religions - Hinduism, Buddhism, and Islam. Buddhism began in India and spread to other places in Asia. Islam came into India from West Asia. The origins of Hinduism are less clear, but are certainly related to the arrival of the Indo-European Aryans from West Asia.
We don't know very much about the earliest Indian religion, of the Harappa people, but certainly it was polytheistic. Based on the art of that time, some people think the later Hindu gods were already being worshipped.
With the arrival of the Aryans about 1500 BC, the Indo-European gods entered India as well. This was the beginning of modern Hinduism. Hinduism was (and is) polytheistic - Hindus believe in many gods. Stories about these gods were written down in the Rig Veda and other epic poems. In this kind of Hinduism, people believed in reincarnation - that people could be reborn into other bodies after they died.
But in the 600s BC, Indian people were interested
in some other way to get a good rebirth than through sacrifice and the
priests. This search is seen in the Bhagavad Gita,
written about this time. And it is seen in the teachings of the Buddha
in the 500s BC. According to Gautama Buddha, people can get free of
the cycle of reincarnation and achieve nirvana by being good people, by learning not to
care about the things of the body, and through meditation. Buddhism
became very popular in India and quickly spread throughout East
Asia. But even Buddhists still paid attention to the Hindu gods.
About the same time, another religious leader, Mahavira, also encouraged people to try to get out of the cycle of reincarnation. His followers were called Jains. Jains thought that the best way to escape reincarnation was to be good - to be kind to people and animals, and to tell the truth, and not to be greedy.
By the 600s AD, even though Buddhism remained popular
in East Asia, many people in India had begun to go back to Hinduism.
They still remembered the Buddha, but he became just one of many Hindu
gods to them. Jainism continued, but among a small group of people in India.
In the 1100s AD, Indian people began to convert to Islam under a series of conquests by Muslim people from the north. Islam demanded that people give up worshipping any god but Allah, and so many people did give up their old Hindu gods at this time. But many people, especially in southern India, also stayed Hindus.
To find out more about Indian religions, check out these books from Amazon or from your public library: