As one Pakistani historian in UK writes:
“The roots of the civil war in 1971 are of course in the partition of 1947 and the establishment of Pakistan. Since Muhammad Ali Jinnah wanted a partition on the basis of religion alone, East and West Pakistan came into being, despite the thousand mile distance and different racial, cultural and political inheritances — the only common thread was the fact that both wings were a Muslim majority. In a way, the success or failure of this experiment was the practical test of the two-nation theory. From the beginning, however, there were clear tensions between the two wings. The first one was a clash over national language (to be clear, English was to remain the official language). The Bengalis, with thousands of years of culture behind them, obviously wanted their language recognised as coequal to Urdu, not least because they did not speak Urdu. Nevertheless, Jinnah categorically refused the Bengali demand in his speech at Dacca University in February 1948, igniting the flame of linguistic nationalism. It is, of course, an irony that Jinnah himself was never fluent in Urdu and spoke mostly in English to the Bengali crowd.”