The Indo-Pakistani War of 1971 was a military confrontation between India and Pakistan that occurred during the Bangladesh Liberation War in East Pakistan from 3 December 1971 until the

Pakistani capitulation in Dhaka on 16 December 1971. The war began with Pakistan's Operation Chengiz Khan which was preemptive aerial strikes on 11 Indian air stations, which led to the commencement of hostilities with Pakistan and Indian entry into the war for independence in East Pakistan on the side of Bengali nationalist forces, expanding the existing conflict with Indian and Pakistani forces engaging on both eastern and western fronts. Thirteen days after the war started, India achieved a clear upper hand, the Eastern Command of the Pakistan military signed the instrument of surrender on 16 December 1971 in Dhaka, marking the formation of East Pakistan as the new nation of Bangladesh. Approximately 93,000 Pakistani servicemen were taken prisoner by the Indian Army, which included 79,676 to 81,000 uniformed personnel of the Pakistan Armed Forces, including some Bengali soldiers who had remained loyal to Pakistan. The remaining 10,324 to 12,500 prisoners were civilians, either family members of the military personnel or collaborators (Razakars).It is estimated that members of the Pakistani military and supporting pro-Pakistani Islamist militias killed between 300,000 and 3,000,000 civilians in Bangladesh. As a result of the conflict, a further eight to ten million people fled the country to seek refuge in India.During the 1971 Bangladesh war for independence, members of the Pakistani military and supporting pro-Pakistani Islamist militias called the Razakars raped between 200,000 and 400,000 Bangladeshi women and girls in a systematic campaign of genocidal rape.

The Bangladesh Liberation War (Bengali: মুক্তিযুদ্ধ, pronounced [mukt̪iɟud̪d̪ʱo]), also known as the Bangladesh War of Independence, or simply the Liberation War in Bangladesh, was a revolution and armed conflict sparked by the rise of the Bengali nationalist and self-determination movement in erstwhile East Pakistan which resulted in the independence of Bangladesh. The war began when the Pakistani military junta based in West Pakistan under the orders of Yahya Khan launched Operation Searchlight against the people of East Pakistan on the night of 25 March 1971, initiating the Bangladesh genocide. It pursued the systematic annihilation of nationalist Bengali civilians, students, intelligentsia, religious minorities and armed personnel. The junta annulled the results of the 1970 elections and arrested Prime minister-designate Sheikh Mujibur Rahman. The war ended on 16 December 1971 when the military forces of West Pakistan that were in Bangladesh surrendered in what remains to date the largest surrender of soldiers since the Second World War.Rural and urban areas across East Pakistan saw extensive military operations and air strikes to suppress the tide of civil disobedience that formed following the 1970 election stalemate. The Pakistan Army, which had the backing of Islamists, created radical religious militias — the Razakars, Al-Badr and Al-Shams — to assist it during raids on the local populace. Urdu-speaking Biharis in Bangladesh (an ethnic minority) were also in support of Pakistani military. Members of the Pakistani military and supporting militias engaged in mass murder, deportation and genocidal rape. The capital Dhaka was the scene of numerous massacres, including Operation Searchlight and the Dhaka University massacre. An estimated 10 million Bengali refugees fled to neighbouring India, while 30 million were internally displaced. Sectarian violence broke out between Bengalis and Urdu-speaking immigrants. An academic consensus prevails that the atrocities committed by the Pakistani military were a genocide.

The Bangladeshi Declaration of Independence was broadcast from Chittagong by members of the Mukti Bahini—the national liberation army formed by Bengali military, paramilitary and civilians. The East Bengal Regiment and the East Pakistan Rifles played a crucial role in the resistance. Led by General M. A. G. Osmani and eleven sector commanders, the Bangladesh Forces waged a mass guerrilla war against the Pakistani military. They liberated numerous towns and cities in the initial months of the conflict. The Pakistan Army regained momentum in the monsoon. Bengali guerrillas carried out widespread sabotage, including Operation Jackpot against the Pakistan Navy. The nascent Bangladesh Air Force flew sorties against Pakistani military bases. By November, the Bangladesh forces restricted the Pakistani military to its barracks during the night. They secured control of most parts of the countryside.The Provisional Government of Bangladesh was formed on 17 April 1971 in Mujibnagar and moved to Calcutta as a government in exile. Bengali members of the Pakistani civil, military and diplomatic corps defected to the Bangladeshi provisional government. Thousands of Bengali families were interned in West Pakistan, from where many escaped to Afghanistan. Bengali cultural activists operated the clandestine Free Bengal Radio Station. The plight of millions of war-ravaged Bengali civilians caused worldwide outrage and alarm. India, which was led by Indira Gandhi, provided substantial diplomatic, economic and military support to Bangladeshi nationalists. British, Indian and American musicians organised the world's first benefit concert in New York City to support the Bangladeshi people. Senator Ted Kennedy in the United States led a congressional campaign for an end to Pakistani military persecution; while U.S. diplomats in East Pakistan strongly dissented with the Nixon administration's close ties to the Pakistani military dictator Yahya Khan.

India joined the war on 3 December 1971, after Pakistan launched preemptive air strikes on North India. The subsequent Indo-Pakistani War witnessed engagements on two war fronts. With air supremacy achieved in the eastern theatre and the rapid advance of the Allied Forces of Mukti Bahini and Indian military, Pakistan surrendered in Dacca on 16 December 1971.

The war changed the geopolitical landscape of South Asia, with the emergence of Bangladesh as the seventh-most populous country in the world. Due to complex regional alliances, the war was a major episode in Cold War tensions involving the United States, the Soviet Union and the People's Republic of China. The majority of member states in the United Nations recognised Bangladesh as a sovereign nation in 1972.