On the other hand, we did take "Population Boom" as a trait during customization. While the Victorian Civil War certainly created mass waves of refugees, I think taking the population boom meant we are generally seen as a attractive migration target. While I think there are conditions (collapsing living standards) and measures (migration controls) that could stop this trait, it still in effect.
This seems to me like that anytime massive numbers of refugees or migrants are created within our geographical area, we are going to receive a larger number than expected otherwise from them. So while the population boom isn't guaranteed, the population is very likely to boom if the conditions are right due to this national spirit and migration will impact us more than it would otherwise.
So, seems like expanding our economy to be able to care for the new citizens will take constant effort. On the bright side, this also gives us economic opportunities. If we manage to get large-scale production of labor intensive goods, we might get internationally competitive trading goods instead of being limited to exporting raw material. Without horribly exploiting the population! The rust belt might become a relevant production hub again.