Doing a wee bit research, these are the basics. In 1947, British India was partitioned into India and Pakistan. The division was made according to religious majorities, India being mainly Hindu and Pakistan being mainly Muslim. The eastern Indian state of Bengal was split into East and West Bengal with East Bengal being part of the new Pakistan .
In 1955, Pakistan became West Pakistan and East Bengal became East Pakistan. The populations were roughly equal but a thousand miles apart. The majority language was Bengali but the official language until 1964 was the Urdu as spoken in West Pakistan. Although East Pakistan produced 70% of the nation�s exports, it received only 25% of the income. The capital was based in West Pakistan and the military and Civil Service were dominated by West Pakistanis.
Resentment of the West Pakistan domination increased and in December 1970, the political party called the Awami League won the majority of Pakistan�s National Assembly seats but they won none in West Pakistan. In West Pakistan, the Pakistan People�s Party (PPP) won the majority of seats but its leader refused to accept an Awami League government and proposed two Prime Ministers.
The President postponed the first session of the new Assembly under pressure from the PPP and calls for independence in East Pakistan grew. The Army, dominated by West Pakistanis, launched an operation on 25th March 1971 against Nationalists with estimates of up to 3,000,000 casualties.
Independence for the new Bangladesh (meaning country or land of Bengal)was declared the following day and the violence continued. India supported the new country and when its forces began to mount on the borders, Pakistan launched an attack against them on 3rd December. India responded with much greater success and Pakistan surrendered in Bangladesh on 16th December.
Does that help any?