Bengal was divided into East and West parts in 1947 when British India was separated into the countries of Pakistan and India , the eastern parts becoming East Bengal , one of the five provinces of Pakistan ( the others being West Punjab , Sind , Baluchistan , and the North-West Frontier Province ) . East Pakistan was created from Bengal Province based on the ` Mountbatten Plan ' in what was then British India in 1947 . Eastern Bengal was given to the Dominion of Pakistan and became a province of Pakistan by the name East Bengal .