Well, this is controvesial subject so I will try to restrain myself. But PPP was without doubt secuar and progressive. However it tripped because it tried to roll back the Urdu speakers gouging of Sindh's urban space. The 1947-57 period had effectively encouraged mass migration from India so that a big slice of the new state and the nascent economy could be captured. This was done with amazing efficiency. So much that by 1955 most of Sindh's urban areas had become effectively colonized by migrants.
The inertia of the grab continued under guise of Islam. The Hindu was demonized as often his property was grabbed. When all it was simple loot and grab. In this Islamic utopia the definition of a 'Muslim' was a Urdu speaker and culture of Lucknow was planted in Pakistan. Hatred for the evil Hindu was institutionalized.
However Gen Ayub's take over began the roll back of this grab. Under his government the capital was shifted and Pakhtuns got a chance to grab a slice. The migrants continued to tout Islam as a cover to consolidate and make their grab 'halal'. The migrants were the most secular and socially liberal in their private sphere. So for instance female education was a accepted and aspired. This was not surprising because many came from urban areas of India with higher literacy rates.
However bizzarely this group socially liberal was the biggest supporter of Islam and Islam parties. This contrasts with socially backward Sindhi's or Pakhtuns from whom had risen secular and even socialists movements. PPP is a good example. The migrants supported Jamaat i Islami etc.
It was these religious parties with street power supported by migrants class who were crucial in bringing Ayub Khan's government down. Underlying it was the ethnic politics as their space was being squeezed begining with the capital being shifted closer to the Pakhtun-Punjabi heartlands.
As Bhutto took over he also began squeezing the migrant space by inducting Sindhi's and made Sindhi language official in Sindh. This seems entirely sensible. I am sure each state in India uses it's own language. It would be logical for Tamil to be the official language of Tamil Nadu.
But this caused reaction from the migrant class who now regarded the grab that they had achieved in 1947-1955 as their birthright. They could grab by using the excuse of Islam but nobody dare roll it back or he was a traitor to Pakistan and un-Islamic.
By 1978 these groups had brought Bhutto down. Jamaat Islami again was instrumental. Gen Zia then in a disgusting, cynical ploy hanged Bhutto. There is enough suspicion that America supported this. By pushing out the left leaning PPP the ground now was cleared for right wing groups.
Gen Zia incubated the MQM as a hedge against PPP in Sindh. This was quite easy because the migrants saw a opportunity to secure their grab under MQM. This party as we all know then kept the grab going all the way until recently.
By this stage politics of religion had been injected to the national bloodline. And here we are today. However the basic driver is economics and power. Each group has used Islam as a ploy to grab power. Below all this 70 year drama is just ethnic and regional power grab and fight for resources of the state. All the poor idiots running around are actually just victims.
Today you can see this on a electoral map of Pakistan. We have BAP in Balochistan, PPP in interior Sindh, MQM mutations in Karachi and Hyderabad [urban Sindh], KPK is mostly PTI, upper Punjab is PMLN. PTI has managed to bite outside KPK and thus managed to form a government by building a coalition. This exposes the harsh reality.
I would suggest you read [below] and it will expose everything.
Migrants and Militants
Fun and Urban Violence in Pakistan
By
Oskar Verkaaik · 2004
View attachment 735330