Northeast India is the eastern-most region of India. It is connected to East India via a narrow corridor squeezed between independent nations of Bhutan and Bangladesh. It comprises the contiguous Seven Sister States (Arunachal Pradesh, Assam, Manipur, Meghalaya, Mizoram, Nagaland, and Tripura), and the Himalayan state of Sikkim. Except for the Goalpara region of Assam, the rest did not become part of political India until the 19th century and later. The Brahmaputra valley area of Assam became a part of British India in 1824, with the hill regions annexed later. Sikkim was annexed to the Indian union through a referendum in 1975; it was recognized as part of Northeast India in the 1990s.