In the German case the important number here isn’t the country’s total population, currently 82 million. It’s the twentysomething population, which was less than 10 million in 2013 (and of course already included many immigrants). In that cohort and every cohort afterward, the current influx could have a transformative effect.
How transformative depends on whether these men eventually find a way to bring brides and families to Europe as well. In terms of immediate civil peace, family formation or unification offers promise, since men with wives and children are less likely to grope revelers or graffiti synagogues or seek the solidarity of radicalism.
But it could also double or treble this migration’s demographic impact, pushing Germany toward a possible future in which half the under-40 population would consist of Middle Eastern and North African immigrants and their children.
If you believe that an aging, secularized, heretofore-mostly-homogeneous society is likely to peacefully absorb a migration of that size and scale of cultural difference, then you have a bright future as a spokesman for the current German government.