Religion has its role in bonding the provinces of Pakistan but beside with religion a Pakistani culture has also evolved in the last 63 years that keep the people glued of all provinces.
Have not you noticed the commonalities between us ?
Urdu the national language is understood and spoken in all parts of Pakistan.
Our national dress is Shalwar+qameez that is used by all from khyber to karachi.
Cricket is a game that is loved by all and everybody forgets about his/her ethnicity and feel a proud Pakistani when our team wins a match. Our food habits are same and one can find the same food wheather in Peshawar, Lahore, Quetta or karachi. Our heros are same in the entertainment world and most of our national leaders enjoy popularity in every part of the country. We have Newspapers that are distributed and read from Gilgit to karachi the same day. We have fashion designers that have their outlets in all provinces and people like the same fashion and style that is popular in other provinces. And there are several other examples that shows the presence of a strong PAKISTANI CULTURE that has bonded all the provinces and people with a common heritage. The minorities of pakistan also practice this culture although they are non-muslim and found in all provinces which shows that beside with religion, we have a common culture that bring us togather.
So beside with religion, it is our common HERITAGE and CULTURE that bonded us togather as one NATION.

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/// Aur be ghum hain zamanay main muhabat kay siwa ///