The Bangladesh Liberation War (Bengali: , pronounced [muktiuddo]), 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 militiasthe Razakars, Al-Badr and Al-Shamsto 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 Bahinithe 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.

East Pakistan was a Pakistani province established in 1955 by the One Unit Policy, renaming the province as such from East Bengal, which nowadays is split up between India and Bangladesh. Its land borders were with India and Burma, with a coastline on the Bay of Bengal. East Pakistanis were popularly known as "Pakistani Bengalis"; to distinguish this region from India's state West Bengal (which is also known as "Indian Bengal"), East Pakistan was known as "Pakistani Bengal". In 1971, East Pakistan became the newly independent state Bangladesh.

East Pakistan was renamed from East Bengal by the One Unit scheme of Pakistani Prime Minister Mohammad Ali of Bogra. The Constitution of Pakistan of 1956 replaced the Pakistani monarchy with an Islamic republic. Bengali politician H. S. Suhrawardy served as the Prime Minister of Pakistan between 1956 and 1957 and a Bengali bureaucrat Iskander Mirza became the first President of Pakistan. The 1958 Pakistani coup d'état brought general Ayub Khan to power. Khan replaced Mirza as president and launched a crackdown against pro-democracy leaders. Khan enacted the Constitution of Pakistan of 1962 which ended universal suffrage. By 1966, Sheikh Mujibur Rahman emerged as the preeminent opposition leader in Pakistan and launched the six-point movement for autonomy and democracy. The 1969 uprising in East Pakistan contributed to Ayub Khan's overthrow. Another general, Yahya Khan, usurped the presidency and enacted martial law. in 1970, Yahya Khan organised Pakistan's first federal general election. The Awami League emerged as the single largest party, followed by the Pakistan Peoples Party. The military junta stalled in accepting the results, leading to civil disobedience, the Bangladesh Liberation War and the 1971 Bangladesh genocide. East Pakistan seceded with the help of India.

The East Pakistan Provincial Assembly was the legislative body of the territory.

Due to the strategic importance of East Pakistan, the Pakistani union was a member of the Southeast Asia Treaty Organization. The economy of East Pakistan grew at an average of 2.6% between 1960 and 1965. The federal government invested more funds and foreign aid in West Pakistan, even though East Pakistan generated a major share of exports. However, President Ayub Khan did implement significant industrialisation in East Pakistan. The Kaptai Dam was built in 1965. The Eastern Refinery was established in Chittagong. Dacca was declared as the second capital of Pakistan and planned as the home of the national parliament. The government recruited American architect Louis Kahn to design the national assembly complex in Dacca.