Creation of Bangalesh is as big a blunder as the incomplete partition of India, ceding of territory to China and to Pakistan.
Pakistan was ruling Bangladesh. Pakistan was hated by Bangaldeshis. And the Paki's had to spend a lot of time and money to control East Bengal.
Once Bangladesh got 'liberated' - we do not have any great friendly relations with it. It is still practically an enemy state of India. It is full of ISI. There are land and river disputes. The border is unfenced and millions of Bangaldeshis flow into India and cause socio-economic problems in India.
It would have been best had Bangladesh remained a part of Pakistan and caused internal problems for Pakistan - rather than have it emerge as an independent entity which is allied with Pakistan and causing problems for India.
