In August 1947, the Partition of British India gave birth to two new states; a secular state named India and an Islamic state named Pakistan. But Pakistan comprised two geographically and culturally separate areas to the east and the west of India. The western zone was popularly (and for a period of time, also officially) termed West Pakistan and the eastern zone (modern-day Bangladesh) was initially termed East Bengal and later, East Pakistan. Although the population of the two zones was close to equal, political power was concentrated in West Pakistan and it was widely perceived that East Pakistan was being exploited economically, leading to many grievances.
In 1948, Mohammad Ali Jinnah, Pakistan's first Governor-General, declared in Dhaka that "Urdu, and only Urdu" would be the sole official language for all of Pakistan. This proved highly controversial, since Urdu was a language that was only spoken in the West by Muhajirs and in the East by Biharis. The majority groups in West Pakistan spoke Punjabi, while the Bengali language was spoken by the vast majority of East Pakistanis. The language controversy eventually reached a point where East Pakistan revolted. Several students and civilians lost their lives in a police crackdown on 21 February 1952.
Although East Pakistan accounted for a slight majority of the country's population, political power remained firmly in the hands of West Pakistanis. Since a straightforward system of representation based on population would have concentrated political power in East Pakistan, the West Pakistani establishment came up with the "One Unit" scheme, where all of West Pakistan was considered one province. This was solely to counterbalance the East wing's votes. East Pakistanis noticed that whenever one of them, such as Khawaja Nazimuddin, Muhammad Ali Bogra, or Huseyn Shaheed Suhrawardy were elected Prime Minister of Pakistan, they were swiftly deposed by the largely West Pakistani establishment.
The situation reached a climax when in 1970 the Awami League, the largest East Pakistani political party, led by Sheikh Mujibur Rahman, won a landslide victory in the national elections. The party won 167 of the 169 seats allotted to East Pakistan, and thus a majority of the 313 seats in the National Assembly. This gave the Awami League the constitutional right to form a government. However, Zulfikar Ali Bhutto (a Sindhi), the leader of the Pakistan Peoples Party, refused to allow Rahman to become the Prime Minister of Pakistan. Instead, he proposed the idea of having two Prime Ministers, one for each wing. The proposal elicited outrage in the east wing, already chafing under the other constitutional innovation, the "one unit scheme".
A planned military pacification carried out by the Pakistan Army — codenamed Operation Searchlight — started on 25 March to curb the Bengali nationalist movement by taking control of the major cities on 26 March, and then eliminating all opposition, political or military, within one month. Before the beginning of the operation, all foreign journalists were systematically deported from East Pakistan. The main phase of Operation Searchlight ended with the fall of the last major town in Bengali hands in mid-May. The operation also began the 1971 Bangladesh atrocities. These systematic killings served only to enrage the Bengalis, which ultimately resulted in the secession of East Pakistan later in the same year. The international media and reference books in English have published casualty figures which vary greatly, from 5,000–35,000 in Dhaka, and 200,000–3,000,000 for Bangladesh as a whole.
Hindu areas suffered particularly heavy blows. By midnight, Dhaka was literally burning, especially the Hindu dominated eastern part of the city. Time magazine reported on 2 August 1971, "The Hindus, who account for three-fourths of the refugees and a majority of the dead, have borne the brunt of the Pakistani military hatred." Sheikh Mujibur Rahman was arrested by the Pakistani Army. General Yahya Khan appointed Brigadier (later General) Rahimuddin Khan to preside over a special tribunal prosecuting Mujib with multiple charges. The tribunal's sentence was never made public, but Yahya caused the verdict to be held in abeyance in any case. Other Awami League leaders were arrested as well, while a few fled Dhaka to avoid arrest. The Awami League was banned by General Yahya Khan.
The violence unleashed by the Pakistani forces on 25 March 1971, proved the last straw to the efforts to negotiate a settlement. Following these outrages, Sheikh Mujibur Rahman signed an official declaration that read:
Today Bangladesh is a sovereign and independent country. On Thursday night, West Pakistani armed forces suddenly attacked the police barracks at Razarbagh and the EPR headquarters at Pilkhana in Dhaka. Many innocent and unarmed have been killed in Dhaka city and other places of Bangladesh. Violent clashes between E.P.R. and Police on the one hand and the armed forces of Pakistan on the other, are going on. The Bengalis are fighting the enemy with great courage for an independent Bangladesh. May Allah aid us in our fight for freedom. Joy Bangla.
Wary of the growing involvement of India, the Pakistan Air Force (PAF) launched a preemptive strike on India. The attack was modeled on the Israeli Air Force's Operation Focus during the Six-Day War. However, the plan failed to achieve the desired success and was seen as an open act of unprovoked aggression against the Indians. Indian prime minister Indira Gandhi declared war on Pakistan and in aid of the Mukti Bahini, then ordered the immediate mobilization of troops and launched the full-scale invasion. This marked the official start of the Indo-Pakistani War. India's external intelligence agency, the RAW, played a crucial role in providing logistic support to the Mukti Bahini during the initial stages of the war. RAW's operations, in then-East Pakistan, was the largest covert operation in the history of South Asia.
On 16 December 1971, Lt. Gen A. A. K. Niazi, Commanding Officer of Pakistan Army forces located in East Pakistan signed the instrument of surrender. At the time of surrender only a few countries had provided diplomatic recognition to the new nation. Over 90,000 Pakistani troops surrendered to the Indian forces making it largest surrender since World War II. Bangladesh sought admission in the UN with most voting in its favor, but China vetoed this as Pakistan was its key ally. The United States, also a key ally of Pakistan, was one of the last nations to accord Bangladesh recognition.
To ensure a smooth transition, in 1972 the Simla Agreement was signed between India and Pakistan. The treaty ensured that Pakistan recognized the independence of Bangladesh in exchange for the return of the Pakistani PoWs. India treated all the PoWs in strict accordance with the Geneva Convention, rule 1925. It released more than 90,000 Pakistani PoWs in five months.
This shows us that though the nation of Pakistan was founded on the basis of religion, it could not sustain itself as a nation just on the grounds of Religion alone. Language is indeed the most important aspect of one's cultural identity. Belgium and Bangladesh have laid down excellent examples for us to comprehend the linguistics strides which persist in India. These were a few examples depicting the notion of Religion versus Language as a basis of foundation of a state.