Earlier quoted context omitted.
Not just 'the West'. https://www.abc.net.au/news/2023-01-21/chinas-population-is-... https://www.theguardian.com/world/2023/jul/26/japan-populati...
Zeihan (geopolitics celebrity dude) talks about this pretty often. It goes hand in hand with urbanization. When you're on the farm and especially when child mortality is high...you have lots of kids as they're needed for work. In the big city, kids are just a costly burden, so people have a lot less. All the countries that jumped into urbanization are in this boat. China, South Korea, Germany, Italy, and Japan are al…
Haredi/Hasidic/ultra-Orthodox Jews are an interesting exception to that – a predominantly urban/suburban subculture sustaining a high TFR (over 6 in Israel).
A stringent religious doctrine which promotes large families may be the only thing which can overcome urbanization's encouragement of lower TFRs. In the long-long-long term, it is possible (not certain) that subcultures with that characteristic will end up numerically dominating the population.
> It's in this decade that they start running out of working age adults and shit starts getting really screwy
The obvious answer is a significant increase in immigration rates. Of course, for political/cultural reasons, some of the countries you mentioned don't want to do that. But, if the economic hardships of population decline grow big enough, they may become bigger than the political/cultural resistance to it.
In the long-long term, that strategy is going to fail, because the immigration source countries are on the same demographic trajectory, just further back on the curve. Still, the point at which it fails may well be long after we are all dead.