A friend of ours was looking for a bride for her brother. She is Hindu, and my wife and I knew another Hindu lady who was looking for a groom for her sister. They were from similar educational and occupational backgrounds, so my wife suggested to her friend that there could be a union here.
We were taken aback when she said that their castes were different: marriage was not possible. We just hadn't thought of that! Although nonplussed, we passed no judgment on their religion or culture: it simply was none of our business. This is how most of us are brought up in South Asia. We regard another person's world-view as irrelevant: that is, we don't regard it at all.
Muslim rule in South Asia lasted centuries, and yet there were no attempts on either side to change the other's culture. Anthropologists claim that the militarily dominant culture tends to assimilate ('acculturate') the local culture if its adherents believe it to be inferior, or the former assimilates itself to the latter if its adherents feel that way. The obvious examples are Europeans in North America, and the Mongols in China, respectively. But I don't know how they would account for Muslim rule in the subcontinent: neither side felt itself to be inferior, or (same thing) superior: they were just -- different.
When Buddhism passed away from the rest of India for reasons that have as much to do with lack of trade and decentralization as with Hinduism's ability to assimilate, a last outpost under the Pala dynasty continued in Bengal during the 8th to 12th centuries. However, they were overthrown by the Vishnu-worshippers, the Senas. Thus, the Buddhist populace had to live under a Hindu monarchy and Hindu elite. (The ruins of a great Buddhist monastery and its adjoining city can still be seen in Bogra, and tourists from Bangladesh and abroad are regular visitors.) Then, in about AD 1200, Muslim invaders from the northwest overthrew the Senas, and Islam found a mass following among the people. In the eastern part of the country--Noakhali, Chittagong, and Sylhet--Arab traders also spread Islamic teaching ('Bangladesh, Encyclopaedia Britannica, 15th Edition). Muslim holy men helped to spread the new religion. Sufis arrived in India and preached Islam, and their tombs today are visited not only by Muslims but people of other religions, especially Hindus.
Things were not the same when the British took over.
The East India Company initially tried to keep the missionaries out. In 1813 the East India Company lost its monopoly of trade with India and was compelled by parliament to allow free entry of missionaries. The Evangelicals, both Anglican and Baptist, were then a rising power in Britain; they found congenial bedfellows in the utilitarianists and even the rationalists -- both these groups wished to 'acculturate' India, considered then as a laboratory for their 'advanced' views. The missionaries encouraged the spread of English, which replaced Persian as the state language, as a prelude to conversion ('India', Britannica). Little did they realize that the 'ethnocide' so successful in North America and Australia would not repeat itself in India in the way they imagined and desired. Nevertheless, it was a massive program of acculturation aimed at culture death.
I personally had the pleasure of meeting a late specimen of the missionary in the person of Angela Robinson, an elderly lady who was stationed at St. Andrew's Mission in Haluaghat, Mymensingh, as an English teacher and education advisor. She wrote a book called 'The History of St. Andrew's Mission, Haluaghat' (Dhaka: Church of Bangladesh, 2002). In her introduction, she observes that one of the reasons that the mission is special is that "Christianity did not come with foreigners but with Bengali and Garo Christians". "I can find no evidence that any foreign missionary had any direct part in the beginning of the Christian community here (p 2)". But that surely begs the question: how did the Bengalis and Garos become Christian in the first place?
A word must be said about the Garos. They were once a nomadic, Mongoloid group who, through various vicissitudes, finally settled among the Garo hills which today are shared by both India and Bangladesh: hence their name. They are animists: they believe that inanimate objects have spirit, and encounter nature not as an 'it' but as a 'thou'. Today, it is natural to feel a nostalgic respect for animism with its inherent respect for nature given the concern, and even panic, over the environment. Henri Frankfort, Thorkild Jacobson and others have noticed and commented on the mythopoeic nature of early Egypto-Mesopotamian civilization. It is a stage of society that we have lost and we cannot but feel a twinge of envy for animists such as the Garos. As expected, they are horticulturalists, practicing slash-and-burn cultivation, livestock farming and hunting.