I have attempted to provide a simple narrative for each form of religion that now find a home in India. All i have presented is some factoids, not a theological discussion of these religions. The main focus has been on numbers, and how India and the particular religion are associated, internally and some external comparison of strength in numbers. Numerical strength here, in my argument, is an indication of acceptance and assimilation, and also a factor to counter or favor as evidence for religious persecution.
India has the largest Hindu population in the world. Hindus form almost 80+% of the country's population. Hinduism is not the religion of the State (government of India). Unfortunately the concept of Hinduism is so tied to the history of India, and it has become indistinguishable from the birth of civilization in India. And much of these early facts about Hinduism, India and its ancient history has been colored by the, now considered bogus, theory of Aryan Invasion. Hinduism, like the indigenous Aryan or Dravidian culture, clearly was born in the sub-continent, and every new site and areas being discovered adds credibility to this fact. More excavations and deciphering the Indus Script will ultimately resolve this once and for all. With around 930 million followers, Hindus would become the fourth largest country in the world, immediately after India !
Jainism is probably one of the oldest religion in the world. This is not including Hinduism, which does not have specific timeline. Jainism also follows a very parallel path, although 900 BCE is often mentioned as the time when it originated. The period beginning around 600 BCE, is when Mahavira became its most influential teacher, and helped Jainism spread throughout most of India. Jainism, like Buddhism, influenced the thinking of Hinduism during its period of prominence. Today there are about 6 million Jains around the world, vast majority of them living in India. The official count of Jains in India is about 5 million. The identity of Jains are difficult to clearly ascertain, as they can be easily counted as Hindus in India and elsewhere, because of customs, particular sects and sub-sects and other idiosyncrasies.
Buddhism is another religion that originated in India. Followers of Buddha and his teachings, instituted from about 600 BCE, and has today about 250-500 million followers worldwide. Buddha was born as Prince Siddhartha in Lumbini, India, and attained enlightenment at Bodh Gaya, India. He lived the rest of his worldly life traveling through most parts of India. Buddhism too had a tremendous impact on the followers of Hinduism, not only because of very closely related ideologies etc, but also because of the compassionate form of the religion. However, today there are only 12 million people within India who are followers of the Buddhist religion. Buddhism was spread by Indian kings through the rest of Asia, to other parts of the globe, where they thrive in larger numbers.
Sikhism is one of youngest religion with a major following. There are about 26 million Sikhs around the world today, and over 22 million of them live in India. Founded by its first guru, fondly called Guru Nanak, in the 1500 CE, it has grown as the 5th largest religion in the world. Skihism is still relatively young compared to the timeline of other religious teachings and followers. Sikhs were mixed with the Hindus and considered another sect of Hinduism by many rulers of India and elsewhere until very recently. It has now been able to establish its true and unique identity.
Zoroastrianism, also known as Parsi in India, has it origins from Persia (today Iran). In 651 CE, with the influence of Islam, and the fall of last non-islamic empire in Persia, Zoroastrians had to migrate out or were slowly but steadily converted to Islam. Large numbers of Zoroastrians landed in the Indian sub-continent, near todays Gujarat and bordering Pakistan. There are only about 200 thousand followers of this faith around the world. The biggest majority live in India, numbering about 70 thousand. A very tight set of rules, that officially does not include conversions, and the practice of inter-community marriages to keep the faith, has resulted in their numbers slowly but steadily declining over the many years.
India is home to more Muslims than only Indonesia, as per 2001 census. As per the most recent available statistics (pending the 2011 census) there are an estimated 165 million Muslims, but that puts India behind only Indonesia and Pakistan. That is more than the population of Bangladesh, Egypt, Iran, Turkey etc. And more than the combined population of Bahrain, Iraq, Jordan, Kuwait, Lebanon, Oman, Palestine, Qatar, Saudi Arabia, Syria, United Arab Emirates and Yemen, the middle-east arab nations. Islam arrived in India, soon after 600 CE, during the lifetime of Prophet Muhammad. The second oldest mosque in the world, exists in India, was built in 629 CE in Kerala, by Cheraman Perumal. Islam spread in India, even before the advent of the Mughals and other invaders who came from the north.
There are over 26 million Christians in India today. That is more than most countries in Europe, except the top 9 (including Russia). Christianity reached in India, probably with the arrival of St. Thomas in 52 CE. Although there is not much information of his evangelism, he is known to have seeded the faith in this country. Christianity's connection with India, runs even deeper, if more proof and facts can be uncovered around the final journey of Jesus, and his apparent life and final burial in Kashmir, India. These facts and incidence show that Christianity or the preachings of Jesus reached India, during his lifetime or immediately after.
It is important to mention the Bahá'í Faith, which also originated outside India, in present day Iran. There are only about 7 million followers of the faith, and almost a third of them, about 2.2 million live in India.
Not leave Judaism behind, India is home to about 15 thousand jews. This number may seem really inconsequential inside India, and also when compared to the world population of Jews numbering a little more than 13 million. However, the real significance is that Jews arrived in India almost 2500 years ago, around 562 BC (