It IS happening here, right now. We are simply not reproducing, political correctness and unrestricted immigration will take care of the rest. Change is constant and ongoing, it will accelerate under the libs and we will continue our slide into the gutter. Sorry to be so negative but evolution is constant too.
The same demographic problem that Europe faces is also faced by America. The native US population is below the replacement rate in fertility. For American whites, it is well below the replacement rate. This is true in all of the industrialized countries of the world, from Europe through Russia to Japan. There aren't any exceptions, and what it tells us is that there is something lethal about the structure of modern industrial economy for its native population.
Fertility below the replacement rate means that a nation will depopulate, and depopulation, once it begins, occurs at the same geometric proportions that growth does (and for the same reasons), unless something causes people to dramatically reverse the fertility decline and start having 4 children per couple on average (do please note that, since children come only in whole units, a replacement rate of 2.2 children per couple means that most couples have to have THREE children, not two, just to meet the replacement rate for the country. To reverse depopulation, many, many more people would have to start having FOUR or MORE children, and this is considered economically impossible to most middle class people across the industrialized world, the US included).
So, the whole industrialized world including the US is depopulating with regards to its native population. And yet a handful of those countries are increasing in population overally, specifically the US, France and the UK.
They do so through massive immigration.
In each case, the immigration brings with it new problems, in particular a problem of political stability and the preservation of the existing country.
In the United States, it is very difficult to see how a rapidly expanding Spanish-speaking population, tied culturally and by family and language to a neighboring nation that bears strong historical grievances against the US, will simply integrate as Italians and Germans once did.
It is far more likely that the rising Mexican minority, eventually will become a plurality and renegotiate the entire American social contract.
The same issue is at work in France, but with considerably less urgency, because the North African population in France is smaller as a proportion of the total, there is no land border, and France has become quite aggressive about stopping illegal immigration. Also, the French are much more willing to impose cultural norms on children in school, and to outright forbid the expression of ideas considered hostile to the Republic. In France, a movement of Arabs who vocally sought the conquest and conversion of France to Sharia would be prosecuted. In the US, there is a strong Reconquista movement that makes no bones about its intent to repopulate the American southwest with Mexicans, and to cause the primary loyalty of that region of the United States to formerly transfer back to Mexico.
Indeed, the eventual threat to the national TERRITORIAL integrity is considerably greater in the United States than in France, when all is considered. However, the degree to which there is a threat of actual national dismemberment is very much ignored by Americans at the present time.
You are correct. Europe has a head start on the fall.
The bright spot is that the illegal immigrants here are Hispanic Christians. In Europe they are Arab Muslims.