This is a very interesting question. Although not familiar with the exact trajectory of India’s demographics over the period, I know of several things that started its population growing beyond what it would have been pre-British colonisation.
Outside the property development and population growth lobby, very few people who are worried about population growth and high immigration appreciate the effect of endogamy (marrying within your people) and exogamy (marrying outside your people) on population size and fertility. They also don’t recognize its effect on the private amassing of wealthy estates and political power. Anyone who wants to understand modern day problems with overpopulation, poverty, and loss of democracy would do well to study this article. This article is intended to stimulate debate about democracy, wealth distribution, and overpopulation. The author invites critical comments and argument.