Pope Francis wants Europe to welcome migrants. Here, from the Pew Forum, is the result by 2050 if his advice is followed:
Here are the fertility rates for religious groups in Austria:
And here is what Vienna would be in a generation, 30% Moslem:
This would be the pattern of most European cities. The Moslem population would also be younger than the general population, and would be the majority of the age group under 40 – the military age.