1971 War:

The internal crisis of Pakistan after the verdict of their general elections in Pakistan turned violent. The ruling party of Zulfikar Bhutto emerged as winner in West Pakistan while in their Eastern Part Sheikh Mujib-Ur Rahman's Awani League won majority of seats with great margins. However, strong and powerful western establishment ignored the democratic verdict and didn't accept the League's demand for federation. Instead of responding to their demands and verdict positively, Pakistan army arrested Rahman and unleashed brutal terror activities and suppressed their voices. To end this menace permanently, people of Eastern Pakistan started liberation struggle of Bangladesh from Pakistan. Due to the huge influx of refugees from Eastern Pakistan, India deliberated much and later extended its support to people's cause materially and morally, which was frowned by Western Pakistan as Indian conspiracy to break of Pakistan.

The support to Western Pakistan came from the USA & China to quash the people's movement. To ensure its safety from the attacks of American and Chinese backed Pak, India signed 20 year Treaty of Peace and Friendship with the Soviet Union. Even after much diplomatic deliberations it could not achieve concrete results, and full scale war broke out in December 1971 on both the western and Eastern front. With the support of local population in the form of "Mukti Bahini" Indian army made rapid progress and compelled the Pakistani troops to surrender in 10 days only. With emergence of Bangladesh as an independent country, India declared a unilateral ceasefire. Later Shimla Agreement of 1972 between Indira Gandhi & Zulfikar Bhutto brought back the peace between two nations. Since then India has argued for Shimla agreement as the framework within which the disputes between the two countries should be resolved.