In 1971, Sheikh Mujibur Rahman, who was then the popular Awami League leader in East Pakistan, won the parliamentary elections, but the Pak army led by Gen Yahya Khan denied him power and threw him into jail.
What followed was a bloody massacre of several lakhs Bengalis by Pak troops in March, 1971 inviting worldwide condemnation. Nearly one crore refugees from East Pakistan took refuge in India.
India openly helped the Mukti Bahini leading to the 14 days' war in December 1971, at the end of which Indian forces occupied Dhaka, and 94,000 Pakistani soldiers led by Lt Gen A A K Niazi surrendered to Indian army.
On the western front, a ceasefire took place, and in 1972, Pak Prime Minister Z A Bhutto signed the Simla Agreement with the then Indian PM Indira Gandhi paving the way for return of all Pak prisoners of war and promised to resolve Kashmir issue through bilateral talks.