You might have noted that many non-Muslim commentators suggest (or hint) that it's a good thing that Muslims in the U.S. and UK are less 'ethnic' than they used to be. Good for whom, exactly? Well, it could actually a bad thing for non-Muslims because it means that Muslims are more uniform and powerful and therefore more politically dangerous. Indeed this is something that many younger Muslims, especially Islamists, stress.
The ummah is a dangerous thing; as Muslims themselves often say (though not in those precise words). When you have Pakistani mosques and Bangladeshi mosques, or even Deobandi and Barelvi mosques, that is a good thing because there is disunity among Muslims. And that's precisely why Islamists, and other Muslims, stress the ummah. A larger and more uniform ummah will give Islamists more power. That is why they detest 'Muslim nationalism' and the 'un-Islamic' stress on Muslim ethnicity. (Though being politicians Islamists, like communists historically, also sometimes use nationalism and ethnicity when they need to.)
Thus Islamists, and many young American and British Muslims, are like International Socialists ('progressives'/ socialists) in that they downplay nationalism/ patriotism and the nation state itself. Islamists are hoping that an increase in the power of the ummah will increase the power of Islamism.