well brother nothing is impossible but in the current circumstances and geo political and geo economic situation it is almost impossible. if you take it as an ideal muslims then its possible under the one "Amir ul Mominin or Caliph" but in today's world when every muslim is thinking just for himself and where one of our brother "East pakistan" get separated from us even being a muslim state we could not treat them justly so how we can talk of unification.

in the long run Inshallah it will happen, like Allama Iqbal says:
"aik hon muslim haram ki pasbani k leay
neel k sahil se le kar tabakhake kashghar"

so we hope that inshallah it will happen and it is the need of the hour and need for existence of Muslim Ummah otherwise it will be perished. Allama Iqbal was a visionary and when writing this "shair" he could see that one day these muslim states will have to unit in order to save themselves as well as their religion.

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When the going is good then everybody is going. But when the going is tough then its the tough who gets going.