Self-determination
In 1947, India gained independence from the British Empire. The empire was in decline but adapted to these circumstances by creating the British Commonwealth—since 1949 the Commonwealth of Nations—which is a free association of equal states. As India obtained its independence, multiple ethnic conflicts emerged in relation to the formation of a statehood during the Partition of India which resulted in Islamic Pakistan and Secular India. Before the advent of the British, no empire based in mainland India had controlled any part of what now makes up the country's Northeast, part of the reason for the ongoing insurgency in Northeast India. In 1971 Bangladesh obtained independence from Pakistan.
Islam in India
The partition of India was set forth in the Indian Independence Act 1947 and resulted in the dissolution of the British Indian Empire and the end of the British Raj. It resulted in a struggle between the newly constituted states of India and Pakistan and displaced up to 12.5 million people with estimates of loss of life varying from several hundred thousand to a million (most estimates of the numbers of people who crossed the boundaries between India and Pakistan in 1947 range between 10 and 12 million). The violent nature of the partition created an atmosphere of mutual hostility and suspicion between India and Pakistan that plagues their relationship to this day.
The partition included the geographical division of the Bengal province into East Bengal, which became part of the Dominion of Pakistan (from 1956, East Pakistan). West Bengal became part of India, and a similar partition of the Punjab province became West Punjab (later the Pakistani Punjab and Islamabad Capital Territory) and East Punjab (later the Indian Punjab, as well as Haryana and Himachal Pradesh). The partition agreement also included the division of Indian government assets, including the Indian Civil Service, the Indian Army, the Royal Indian Navy, the Indian railways and the central treasury, and other administrative services.