It's difficult to look to historic precedent because the heart of all of these issues is fertility. This [1] is a graph of fertility rates in the US. Fertility rates just started plummeting catastrophically in the 60s. The exact same thing happened in the Netherlands. [2]
And that's what's causing the crisis. Fertility rates define not only the population in a region, but also the age distribution. Low fertility rates result in a population that will have many times more elderly people than youthful people, and will start shrinking far more rapidly than most realize. It will lead to both economic and social catastrophe. Trying to use mass immigration as a means of solving this problem is an inherently modern idea, because the problem did not exist in the past.
And IMO this isn't just an issue of management of a nation. Trying to create a stable economy and healthy society with a collapsing fertility rate may well just not be possible. On top of cultural conflicts there's also the fact you'll have to tax the death out of the youth in order to subsidize the elderly, at the same time those youth will find ever shrinking economic opportunities as your economy itself also naturally shrinks.
And that's what's causing the crisis. Fertility rates define not only the population in a region, but also the age distribution. Low fertility rates result in a population that will have many times more elderly people than youthful people, and will start shrinking far more rapidly than most realize. It will lead to both economic and social catastrophe. Trying to use mass immigration as a means of solving this problem is an inherently modern idea, because the problem did not exist in the past.
And IMO this isn't just an issue of management of a nation. Trying to create a stable economy and healthy society with a collapsing fertility rate may well just not be possible. On top of cultural conflicts there's also the fact you'll have to tax the death out of the youth in order to subsidize the elderly, at the same time those youth will find ever shrinking economic opportunities as your economy itself also naturally shrinks.
[1] - https://fred.stlouisfed.org/series/SPDYNTFRTINUSA
[2] - https://www.macrotrends.net/countries/NLD/netherlands/fertil...