East Pakistan as it was known left because the West Pakistan government were not dividing royalties equally or something of that sort. (Not given equal seats in government. I dunno... Haven't read much about it) If the two do reunite, it would help both beneficially. Unlike Pakistan and India, as Mark described. First there are the Religious problems and as well as the difference in economy's. It would not benefit India, where as Bangladesh and Pakistan uniting would help both economically in the long term.