Why did James Mill divide his book, 'The History of British India' into the Hindu, Muslim and British Periods?

According to Mill before the British came to India, Hindu and Muslim dictators ruled the country. There was religious intolerance, caste discrimination and superstitious practices in the Indian society. James Mill felt that only the British could bring enlightenment and happiness to the Indians by refining them. He felt that European culture, arts and law were necessary to uplift the downtrodden Indians.
So, James Mill divided his book into 3 periods; namely the Hindu, Muslim and British; to establish his view that the period before British rule was one of darkness and British rule represented all the forces of progress and civilisation.