Civil war broke out in march 1971 with military crackdown called Operation Searchlight to suppress the unrest after Mujibur Rahman was denied Prime Minister Post, millions of refugees started pouring into India and started a guerrilla warfare under the name Mukti Bahini(comprising of former Pakistani Bengali soldiers who revolted and common people) exhausting Pakistani army in 9 months as they were very much adapted to fight in river plains, deltas and marshland. In November 1971 Pakistan formally declared war against India by bombing certain airfields in North-Western India, soon Americans, Arabs and Chinese got involved indirectly. Americans even sent their 7th fleet in Bay of Bengal to scare India which even involved Soviet Union later on.
thanks I saw dat in wiki. and we believed we had it bad in South Afrika. u people were about to cause a world war lol