There are at-least five different unique races united within Pakistan, each of these races have their own unique cultures, languages and dress with the only commonality among these races being Islam, if Pakistan can not only exist but thrive under such circumstances then I don't see why another race or more can unite with the five who already are united under the banner of Islam.
Islam = Unification = Strength.
Correct me if I am wrong, but wasn't there a sixth race too, up till '71? And that race was also predominantly Muslim, no?
Races and nations do not have fixed definitions. They change over time. Pakistan of today has one race and that is the Pakistani race. There are sub-groups which use a common language to communicate with each other. There are common customs, common cuisine and common cultural traits. Plus there is a very strong, never seen before, sense of patriotism in the younger generation; kids identify themselves as a Pakistani first and then with their province. Moreover the geographical boundaries that existed until a few decades ago are disappearing rapidly, thanks to urbanization (fun fact: more Pashtuns live in Karachi than in Peshawar). So this five races, five ethnicities crap is outdated.
Whether mullahs like it or not, the fact is that Islam is not the force holding Pakistan together. This latest war on terror is a very good example. There are Pakistanis from all provinces on both sides. And the side claiming to be the better Muslims doesn't recognize the State of Pakistan. My point is that ethnicity is not the dividing factor in our costliest war yet, Islam is.