What led to the break-up of Pakistan?
No wonder that after the war when the dust settled, Sheikh Mujibur Rehman came up with his six point formula in the opposition leaders' meeting in Lahore in 1966. The Six-Point formula later became the main plank of the Bangladesh movement, and eventually turned out to be the beginning to the end of the relationship between the two wings of Pakistan.
According to Hasan Zaheer, the author of The Separation of East Pakistan,  given the degree of alienation by the late 1960s, it was in the larger interest of both East and West Pakistan to resolve their differences by either binding themselves in a loose confederation, or act as independent sovereign states. Slogans raised by the leadership to use Islam as a catch-word, could not sustain the unity of Pakistan. The issues were far too important to be resolved by a mediocre leadership. These issues were primarily secular and not religious, and as such they merited resolution in a spirit of tolerance, justice, fair-play, and mutual accommodation by the political leadership.
The second decade of independence (1958-1968) saw the beginning of the end of the united Pakistan. Nothing contributed more to alienation between the two wings of Pakistan than the ten years of Ayub Khan's regime. Effective political power was concentrated in the hands of the Generals and civil bureaucrats, a class in which East Pakistan was poorly represented. The sense of disenchantment in the eastern wing with the centralized system touched its peak under Ayub Khan's regime.
Disparity in development increased during the second and third plan periods because the policies that had created this disparity also continued unchanged. It is a strange but understandable commentary on the irresponsiveness of policy makers to the demands and grievances of East Pakistanis that even though the wave of resentment in East Pakistan against this disparity had been rising ever since the 1954 elections, there was no significant change in these policies. Thus, during the second plan, in terms of actual implementation, the share of East Pakistan in the total public and private sector expenditure was about 32 percent. During the third plan, the share was 36 percent. The figures of development and non-development expenditure in per capita terms are even more graphic. During the third plan (1960-65) the per capita development and revenue expenditures in West Pakistan were Rs. 521.05 and Rs. 390.35, respectively, whereas the expenditures for East Pakistan were as low as Rs. 240 and Rs. 70.29 respectively.  Regional economic disparity provoked bitter opposition and resentment in East Pakistan towards the central government.
East Pakistan often bitterly complained that there were few East Pakistani officers at the highest levels of the civil service. In some of the key ministries associated with economic policy making, particularly at the secretary level, all the officers until 1969 were from West Pakistan or had emigrated from the Muslim-minority provinces of India. East Pakistan also continued to resent the fact that 60 per cent of the Budget (sometimes even more) was allocated for defense in which the eastern wing had only a nominal share.
However, attempts were constantly made to deploy the rhetoric of the Ummah and Islamic statehood as the unifying ideology and instrument of legitimization. As consistently, religion refused to serve the political purpose even among the devout Bengalis. Eventually, official Islam in East Pakistan was reduced to extremist factions -- Badr, Shams, and Jamat -- which were totally isolated from East Pakistan's Muslim majority.
During President Ayub Khan's regime, there was a growing skepticism, both in East and West Pakistan, as to whether the appeal to Islamic sentiments could continue to keep the two disparate wings together. It was becoming apparent that Islam could neither be aroused to justify nor explain the increasing in egalitarian society that had emerged in West Pakistan nor as the only cementing force between the two disparate wings of the country. An appeal to religion had lost its strength, and it was clear that Bengali aspirations would be satisfied within the existing political framework if the economy had to satisfy the increasing expectations of West Pakistan as well.
Ayub Khan failed to satisfy the Bengali expectations that he had aroused through his constitutional assurances to remove disparity. At one time President Ayub Khan's regime even suggested secession to an East Pakistani leader. According to Justice Munir : "When in 1962, I joined Ayub's cabinet as a law minister for a short time, I found that no constructive work was being done by the assembly. Everyday was spent in listening to the long speeches of East Pakistan members of exploitation of East Pakistan.... I spoke to Ayub and suggested that there could be no fusion between, or common goal between the two provinces and asked him whether it would not be better, to ask East Pakistan to take their affairs in their own hands instead of putting up with this nonsense. He suggested to me that I should talk about it to some influential leader from East Pakistan. One day while I was talking to Mr. Ramizuddin, who has been a Minister in Bengal or East Pakistan, I broached the matter to him. His reply was prompt and straight. He asked me whether I was suggesting secession. I said yes to something like it as confederation or more autonomy. He said 'Look, here we are the majority province and it is for the minority province to secede because we are Pakistan.' The matter ended there and complaints in the Assembly continued as before."
East Pakistan came to experience what seemed to them to be a colonialist domination by a remote alien element, who neither understood nor sympathized with their aspirations and who as they believed, deprived them of what they regard as their fair share of investment and economic development.
The essential differences between the two wings were further confirmed by the conflict between the Six Points program of the Awami League and the principles and the procedure laid down in the Legal Framework Order issued by President Yahya Khan on 28th March, 1970. Both agreed that Pakistan should be a federal republic but the differences lay in the concept of the central government.
The Six Points declared that the federal government should be responsible only for defense and foreign affairs; there should be two separate mutually convertible currencies or, if one currency, there should be regional reserve banks to prevent the transfer of resources and flight of capital from one region to the other. Fiscal policy was to be the responsibility of the federating units, who were to provide the central government with the necessary resources for defense and foreign affairs. The regional governments were to be responsible for foreign trade and aid, and were to be empowered to maintain their own militia or para-military force.
The 'fundamental principles' in the Legal Framework Order proclaimed that 'Pakistan shall be so united in a federation that the independence, the territorial integrity and the national solidarity of Pakistan are ensured, and that the unity of the federation is not in any way impaired.' The provinces were to have maximum autonomy, that is to say maximum legislative, administrative and financial powers, but the federal government was to have 'adequate powers, including legislative, administrative and financial powers, to discharge its responsibilities in relation to external and internal affairs and to preserve the independence and integrity of the country.'
There was an obvious conflict here. The exclusion of foreign trade and aid from the purview of the central government as proposed by Six Points, would deprive it of real control over foreign policy, and its inability to levy by the provinces. The Awami League leaders never succeeded in showing convincingly how the Six Points would give the central government any real control over foreign affairs and defense.
In spite of these implications of the Six Points, President Yahya Khan allowed the Awami League to campaign on the basis of the Six Points. He could hardly have been expecting to foresee Sheikh Mujibur Rehman's astonishing victory in the subsequent elections, giving the Awami League an absolute majority in the Assembly. Perhaps, Yahya Khan did not choose to settle the Six Points issue because he was led to believe by his intelligence agencies, as also by the political party supporting him, the Jamaat-i-Islami in East Pakistan, that no single political party, including the Awami League, would win an absolute majority. There would be a number of parties, splinter groups and individuals with a sizable number of seats in the National Assembly and that as President, Yahya Khan would be able to bargain from a position of strength and play off one against the other.
In short, General Yahya Khan held elections but refused to hand over power to the party which had gained a clear majority. In this, the Generals around him as well as some West Pakistan-based politicians, including Zulfikar Ali Bhutto, gave him due encouragement.
No doubt the secession of East Pakistan was the anti-climax of the long story of political maneuvering, social injustices and economic deprivation. Available information and data suggests that this dissension arose mainly because the power elites of West Pakistan formulated certain policies that provoked as much opposition and bitterness from the East that the system was brought to the verge of collapse. However, the dismemberment of Pakistan was also linked with a wider conflict involving the five most populous countries in the world -- China, the Soviet Union, the United States and India and Pakistan. Thus the Indo-Pakistan war on Bangladesh in 1971 'was not only another phase in the long religious conflict between Muslims and the Hindus, not merely a moral conflict between Pakistan's vicious suppression of the Bangladeshi rebels and India's calculated military aggression to dismember the Pakistani state. Back of all this, there was a power struggle between China and the Soviet Union and a strategic struggle between Moscow and Washington.
In the closing phase of the civil war in East Pakistan, the US Secretary of State, Henry Kissinger, is believed to have informed India of Pakistan's willingness to discuss a timetable for the grant of complete provincial autonomy to the eastern wing and in mid-November 1971, a secret five-point peace plan is said to have been given by Yahya Khan to the Indian Ambassador in Islamabad. The plan included a provision for a referendum on the issue of East Pakistan's independence. Indian Prime Minister Mrs. Indira Gandhi nevertheless declined it and her army, along with Mukti Bahni (the irregulars supporting East Pakistan's bid for independence) pressed on until the Pakistani forces were forced to surrender in Dhaka on December 16.