War of Liberation, The began on 26 March 1971 and ended with the liberation of Bangladesh on 16 December 1971. The armed struggle was the culmination of a series of events, situations and issues contributing to the progressively deteriorating relations between East and West Pakistan. The questions of land reforms, state language, inter-wing economic and administrative disparities, provincial autonomy, the defense of East Pakistan and many other consequential questions had been straining the relations between the two wings of Pakistan ever since independence of the country from Britain in 1947.
In 1948, Governor-General Muhammad Ali Jinnah declared that "Urdu, and only Urdu" would be the federal language of Pakistan. However, Urdu was historically prevalent only in the north, central, and western region of the subcontinent; whereas in East Bengal, the native language was Bengali, one of the two most easterly branches of the Indo-European languages. The government stand was widely viewed as an attempt to suppress the culture of the eastern wing. The people of East Bengal demanded that their language be given federal status alongside Urdu and English. The Language Movement began in 1948, as civil society protested the removal of the Bengali script from currency and stamps, which were in place since the British Raj. The movement reached its climax in 1952, when on 21 February, the police fired on protesting students and civilians, causing several deaths.
Although East Pakistan had a larger population, West Pakistan dominated the divided country politically and received more money from the common budget.
Bengalis were under-represented in the Pakistan military. Officers of Bengali origin in the different wings of the armed forces made up just 5% of overall force by 1965; of these, only a few were in command positions, with the majority in technical or administrative posts. West Pakistanis believed that Bengalis were not "martially inclined" unlike Pashtuns and Punjabis; the "Martial races" notion was dismissed as ridiculous and humiliating by Bengalis. Moreover, despite huge defense spending, East Pakistan received none of the benefits, such as contracts, purchasing and military support jobs. The Indo-Pakistani War of 1965 over Kashmir also highlighted the sense of military insecurity among Bengalis, as only an under-strength infantry division and 15 combat aircraft without tank support were in East Pakistan to thwart any Indian retaliations during the conflict. 
The only common bond between the two Pakistani wings was religion. But there were differences even in religious practices. Bengali Muslims tended to be less conservative in religious zeal, and had come to accept their Hindu minority and neighbors despite some communal clashes. Many Bengali Muslims strongly objected to the Islamist paradigm imposed by the Pakistani state. Most members of West Pakistan's ruling elite also belonged to a liberal society, yet understood a common faith as the mobilizing factor behind Pakistan's creation and the subsuming of Pakistan's multiple identities into one. 
The military forces killed everybody in sight on the footpath and destroyed everything on their way. The tanks roared through the streets of Dhaka blasting indiscriminately at the people and official and residential buildings. They gunned down clusters of settlements and set fire on them. Scores of artillery bursts were pounded, while the tanks rumbled into the city roaring the main streets. The student halls of residence at Dhaka University were raided and numerous students residing there were brutally killed and maimed. They also killed many teachers of Dhaka University. The Hindu concentrated areas of old Dhaka were particularly targeted. They started killing the people, burnt their houses, looted their valuables and raped their women. The genocide that was perpetrated on the unarmed people was flashed in the world press. On the night of 25 March Sheikh Mujibur Rahman was taken prisoner by the Pakistan army.
There were spontaneous uprisings throughout Bangladesh following the declaration of independence on 26 March 1971. These uprisings were participated by government officials, political activists, students, workers, peasants, professionals and members of the public. After initial resistance, many freedom fighters crossed over into Indian territory to have safe sanctuary, due mainly to the enemy's overwhelming superiority of trained soldiers and modern weapons. The scattered and temporarily retreating rudimentary liberation forces were soon brought under a unified command.
On 4 April, the senior officers of the liberation army assembled at the headquarters of 2nd East Bengal at Teliapara, a semi hilly area covered by tea gardens where Colonel MAG Osmany, Lieutenant Colonel Abdur Rob, Lieutenant Colonel Salahuddin Mohammad Reja, Major Kazi Nuruzzaman, Major Khaled Mosharraf, Major Nurul Islam, Major Shafat Jamil, Major Mainul Hossain Chowdhury and others were present. In this meeting four senior commanders were entrusted with the responsibility of operational areas. Sylhet-Brahmanbaria area was placed under the command of Major Shafiullah. Comilla-Noakhali area was given to Major Khaled Mosharraf while Chittagong-Chittagong Hill Tracts was given to Major Ziaur Rahman. Kushtia-Jessore area was placed under command of Major Abu Osman Chowdhury. In the meeting the organisational concept of the freedom fighter forces and the command structure were chalked out. Colonel MAG Osmany was to command the liberation forces, later named as MUKTI BAHINI.
An exile government called the People's Republic of Bangladesh Government alias MUJIBNAGAR GOVERNMENT was formed on 10 April with Bangabandhu Sheikh Mujibur Rahaman as President of the Republic, Syed Nazrul Islam as Vice President and Tajuddin Ahmed as Prime Minister. On the day following Tajuddin Ahmed announced the names of three more regional commanders, Captain Newazish for Rangpur region, Major Najmul Haque for Dinajpur-Rajshahi-Pabna and Major Jalil for Barisal-Patuakhali region. All these regions were later named as sectors. All of Bangladesh was divided into eleven such sectors and different sub-sectors for operational purposes during the Sector Commander's conference held from 10 to 17 July 1971.
On 27 March, Prime Minister of India Mrs. Indira Gandhi expressed full support of her government to the freedom struggle of the Bangalis. Indian Border Security Force (BSF) opened Bangladesh-India border to allow the tortured and panic stricken Bangalis to have safe shelter in India. The governments of West Bengal, Bihar, Assam, Meghalaya and Tripura established refugee camps along the border. These camps became ready ground for recruitment of the freedom fighters. The students, peasants, workers and political activists joined the Mukti Bahini with high spirit to liberate Bangladesh from the Pakistan army. They were given training on tactics and the use of arms and explosives. On completion of training, they were posted to different sectors to fight the enemy. The headquarters of the Bangladesh Forces was established at 8 Theatre Road, Calcutta which started functioning from 12 April 1971. Lieutenant Colonel M A Rab and Group Captain A K Khandaker were appointed as Chief of Staff and Deputy Chief of Staff respectively.
Besides Mukti Bahini, many other bahinis were organised inside Bangladesh at different places to fight Pakistan Army. These Bahinis included Kader Bahini of Tangail, Latif Mirza Bahini of Sirajganj, Akbar Hossain Bahini of Jhinaidah, Hemayet Bahini of Faridpur, Quddus Molla and Gafur Bahini of Barisal, Afsar Bahini of Mymensingh and Aftab Bahini of Mymensingh. A crack platoon consisting of daring youths operated most valiantly in Dhaka city as well. These bahinis were established as a local force based on their own strength taking part in a number of battles with the occupation army. Siraj Sikdar, leader of Sarbahara Party, also organised his force in Barisal. Another Bahini named as Mujib Bahini was organised in India with the active assistance of Major General Oban of the Indian army who was an expert in guerilla warfare. Mujib Bahini was trained at Dehradun. Student League leaders Sheikh Fazlul Haq Mani, Tofael Ahmed, Abdur Razzak and Sirajul Alam Khan were organisers of this Bahini.
Mukti Bahini consisted of the regular and the irregular forces. The regulars were later called 'Niamita Bahini' (regular force) and the irregulars were called 'Gana Bahini' (people's force). The regulars included East Bengal Regiment and EPR troops. The irregular forces, which after initial training joined different sectors, consisted of the students, peasants, workers and political activists.
Irregular forces were inducted inside Bangladesh territory to adopt guerilla warfare against the enemy. The regular forces were engaged in fighting in conventional way. The first conventional brigade named as 'Z' Force was created in July. Major Ziaur Rahman was appointed commander of this brigade and the brigade was named as 'Z' Force after the first letter of his name. This brigade consisted of 1, 3 and 8 East Bengal. Second regular brigade 'S' Force was created in October and consisted of 2 and 11 East Bengal. 'S' Force was named after the initial letter of the name of its commander Shafiullah. Similarly the 'K' Force created with 4, 9 and 10 East Bengal was commanded by Khaled Mosharraf.
Bangladesh Air Force, which was organised by Air Commodore A K Khondaker, was created in Dimapur of Nagaland on 28 September. Squadron Leader Sultan Mahmud, Flight Lieutenant Badrul Alam, Captain Khaleq, Sattar, Shahabuddin, Mukit, Akram and Sharfuddin and 67 airmen initially joined the Bangladesh Air Force, which had only few Dakota, Auter type air plane and Aluvet helicopters.
Similarly, Bangladesh Navy was also established with the Naval troops deserted from the Pakistan Navy. On 9 November 1971, the first naval fleet 'Bangabandhu Naubahar' consisting of six small ships was inaugurated. The command structure of the Bangladesh Forces was fully organised with the regular brigades, sector troops and guerilla forces, the Bangladesh Air Force and the Navy.
The Mukti Bahini had fought many successful battles in putting up initial resistance. But within a short time, they were temporarily contained by the Pakistan army and were compelled to withdraw to the safe sanctuary in the Indian territory. The Mukti Bahini was, however, re-equipped, reorganised and retrained. As a result, it got into fighting with fresh zeal after April-May 1971.
At the international level, the United States of America and the People's Republic of China considered the crisis as an internal affair of Pakistan. On the other hand, India, Soviet Union and her allies, and general masses in Japan, and Western countries stood solidly behind Bangladesh. In order to gain strategic advantage vis-a-vis Sino-US-Pakistan axis, Indo-Soviet Friendship Treaty was signed on 9 August 1971. It provided a new dimension to the War of Liberation.
Having realised that the Pakistan army could not be defeated by conventional warfare method, it was decided to create large guerilla forces all over the country. All Sector commanders were accordingly ordered to recruit, train and induct guerillas inside the country.
The joint command of the Mukti Bahini and the Indian army was underway from November 1971. Lieutenant General Jagjit Singh Aurora, Commander, Eastern Command of Indian Army, became the commander of the joint forces. The joint command of the Mukti Bahini and the Indian Army, however, started operation from the evening of 3 December, when the Pakistan Air Force bombed Amritsar, Sreenagar and the Kashmir valley. Immediately, the Indian armed forces were ordered to hit back the Pakistan army and thus the Indo-Pak war broke out. The Mukti Bahini and the Indian army continued advancing inside Bangladesh and the defeat and surrender of the Pakistan army became a matter of time. International efforts for a cease-fire failed due to Soviet veto in the United Nations Security Council.
The Indian troops and the freedom fighters of Sector 11 reached Tongi on 14 December, and Savar in the morning of 16 December. Major General Jamshed, commander 36 Division of the Pakistan Army received Major General Nagra at Mirpur Bridge near Dhaka City. The Mukti Bahini and the Indian forces entered Dhaka city at 10.10 a. m. Major General Jacob, the chief of staff of the Indian Eastern Command landed at Dhaka airport at 1 p.m with the draft instrument of surrender.
A fleet of helicopters landed on the tarmac of Dhaka airport at about 4 p.m with Lieutenant General Aurora and his staff. Group captain AK Khandaker, deputy chief of staff, Bangladesh forces, represented the Mukti Bahini. Lieutenant General AAK Niazi received Lieutenant General Aurora. The instrument of surrender was signed by Lieutenant Jagit Sing Aurora and Lieutenant General Niazi at the Ramna Racecourse (now Suhrawardy Udyan) at one minute past 5 p.m on 16 December 1971.
Sectors of War of Liberation In the War of Liberation in 1971 the whole geographical area of the then East Pakistan was strategically divided into eleven sectors with a sector commander for each of them. For better efficiency in military operations each of the sectors were divided into a number of sub-sectors under a commander.
Source of Information: Banglapedia.