America’s foreign policy has always supported dictatorship and theocracies rather than find allies among secular countries like India.
When the British left India, India was divided into Hindu Majority and Muslim Majority as two sovereign nations as India and Pakistan. Pakistan was divided into two parts West and East with India in the middle. In case of East Pakistan who were Bengali speaking Muslims- were not given proper attention by the Pakistan government which focused all its attention on the development of Western Part of Pakistan. The people of East Pakistan (Bangladesh) started to yern for liberation from Pakistan. Yet another important factor was Bengali language identity, since they were against the imposition of Urdu as the official Language. The Bangladeshi people also faced atrocities from their own government, after a long period of genocide and conflict hordes of refugees began to come to India, and Indra Gandhi the then Prime Minister of India had no choice but to intervene in the conflict and help Bangladesh gain freedom from Pakistan in 1971. United States was an ally of Pakistan and for various reasons did not want to help India at this crucial juncture even when Mrs.Indra Gandhi asked for help. It was during such circumstances that India signed a peace treaty with Soviet Union in 1971 and even though India previously had been a non aligned nation.
For More Details Kindly read
1971 India Pakistan War: Role of Russia, China, America and Britain
By Sanskar Shrivastava