Operation Searchlight was the codename for a planned military operation carried out by the Pakistan Army in an effort to curb the Bengali nationalist movement in former East Pakistan in March 1971. Pakistan retrospectively justified the operation on the basis of anti-Bihari violence carried out en masse by the Bengalis earlier that month. Ordered by the central government in West Pakistan, the original plans envisioned taking control of all of East Pakistan's major cities on 26 March, and then eliminating all Bengali opposition, whether political or military, within the following month.

West Pakistani military leaders had not anticipated prolonged Bengali resistance or later Indian military intervention. The main phase of Operation Searchlight ended with the fall of the last major Bengali-held town in mid-May 1971. The operation also directly precipitated the 1971 Bangladesh genocide, in which between 300,000 and 3,000,000 Bengalis were killed while around 10 million fled to neighbouring India as refugees.Bengali intelligentsia, academics and Hindus were significantly targeted alongside Muslim Bengali nationalists, with widespread indiscriminate and extrajudicial killings taking place. The nature of these systematic purges enraged the Bengalis, who declared independence from the union of Pakistan to establish the new nation of Bangladesh.The widespread violence resulting from Pakistan's Operation Searchlight ultimately led to the Bangladesh Liberation War, in which Indian-backed Mukti Bahini guerrillas fought to remove Pakistani forces from Bangladesh. The civil war escalated in the following months as East Pakistani loyalists (mostly from the persecuted Bihari minority) formed militias to support West Pakistani troops on the ground against the Mukti Bahini. However, the conflict took a decisive turn in the Bengalis' favour following the ill-fated Operation Chengiz Khan, which resulted in direct Indian military intervention in the civil war, eventually prompting Pakistan's unconditional surrender to the joint command of Indian forces and the Mukti Bahini on 16 December 1971.

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.