From Indian Summer: The Secret History of the End of an Emperor, by Alex von Tunzelmann (Picador, 2008), pp. 236-238:
Despite his preoccupation with trivialities, even Mountbatten could not ignore the fierce controversies thrown up by the two partitions of Bengal and the Punjab. For centuries, both regions had been melting pots of cultures, a jumbled variety of Muslims and Hindus living side by side, with Sikhs, Buddhists, Animists and Christians fitted in too. In times of peace, it had not mattered much to which of these religions a Punjabi or a Bengali adhered. As Jinnah himself had admitted, most people within the regions tended to consider their local identity before their religious affiliation. But the importance of religious identity had been growing in the twentieth century, notably in India and more slowly in the world beyond it.
The reason for this effect can in part be traced to the British policy of “divide and rule.” Undoubtedly, the raj did plenty to encourage identity politics. The British found it easier to understand their vast domain if they broke it down into manageable chunks, and by the 1930s they had become anxious to ensure that each chunk was given a full and fair hearing. But picking a few random unelected lobbyists, based on what the British thought was a cross-section of Indian varieties, was not a reliable way to represent 400 million people. India’s population could not be divided into neat boxes labeled by religion and cross- referenced with social position. India was an amorphous mass of different cultures, lifestyles, traditions and beliefs. After so many centuries of integration and exchange, these were not distinct, but rippled into each other, creating a web of cultural hybrids and compromises. A Sunni Muslim from the Punjab might have more in common with a Sikh than he did with a Shia Muslim from Bengal; a Shia might regard a Sufi Muslim as a heretic; a Sufi might get on better with a Brahmin Hindu than with a Wahhabi Muslim; a Brahmin might feel more at ease with a European than he would with another Hindu who was an outcaste. When the British started to define “communities” based on religious identity and attach political representation to them, many Indians stopped accepting the diversity of their own thoughts and began to ask themselves in which of the boxes they belonged. At the same time, Indian politicians began to focus on religion as a central part of their policies—defining themselves by what they were, and even more by what they were not.
This phenomenon is shown at its clearest with Jinnah, who began his career as the leading light of Hindu-Muslim unity, and ended it by forcing the creation of a separate Islamic-majority state. But the arc of Jinnah’s career merely amplifies that of Indian politics as a whole. Congress was a largely secular and inclusive organization during Motilal Nehru‘s prime in the first twenty years of the twentieth century. Though it was the opposite of his intention, the emergence of Gandhi gave confidence to religious chauvinists. While Gandhi himself welcomed those of all faiths, the very fact that he brought spiritual sensibilities to the center of politics stirred up extreme and divisive passions. Fundamentalist Hindus were rare presences on the political scene before Gandhi. In the wake of Gandhi, though, Hindu nationalists were able to move into the central ground of politics; while organizations like the Hindu Mahasabha and the Rashtriya Swayamsevak Sangh (RSS), dedicated to the formation of a Hindu nation, swelled their ranks from the fringes. This was no slow, invisible political trend; it was happening visibly during the spring and summer of 1947, when holy sadhus clad in saffron robes marched around the streets of Delhi, bellowing forth political slogans. Rajendra Prasad, who was to become the president of the new Constituent Assembly, wrote to Nehru on 7 August telling him that since July he had received 164,000 letters and postcards demanding that cow slaughter be made illegal—a common concern of devout Hindus, but one which is often used and taken as an anti-Muslim strategy. It was the Muslims in India, and the Untouchables, who ran the lucrative leather and beef industries, mostly for export. The threat of a ban on cow slaughter naturally drove Muslims and Untouchables into the arms of more radical political organizations, which they felt would stick up for them. Whether the British caused division by carving up politics on the basis of religion, or whether they were simply responding to a trend in Indian society for Hindu nationalism and the beginnings of an Islamic resurgence, is an endlessly debatable question.
Far Outliers 
