The common benchmark 'replacement' ratio of birth to death is 2.1.
Once a country falls below that, they're on a slow multi-generational train ride to extinction. There will be multiple stops along the way, where small towns get hollowed out (youngsters move to the cities), and the social safety net for the elderly goes away (not enough money coming in from fewer young, money-earning people).
Next stop is where there aren't enough caregivers for the growing elderly population. After that, you start going down the dark alleys of Senecide, where the elderly are left out in the forest or ignored to die.
None of this is new. Japan and South Korea have been dealing with it for the past 20 years.
Only solution is immigration from high-baby to low-baby regions. But if the culture is closed and xenophobic, they'll put barriers up to slow the flow. Second class citizen status. Sectioned-off neighborhoods. Laws to prohibit inter-racial marriage. That sort of thing. After a few years, those immigrants will trend somewhere safe and financially viable where they will get proper respect.
There will be partial stops, of course, where local nationalists will make angry noises about purity and poisoning bloods of the country, etc and win local elections (👋🏽 USA, Germany, Italy, France, and Netherlands!)
But the hard, long-term reality is: a safe, peaceful life is expensive and the cultural norms putting women down just don't fly any more. The kids are just not making enough babies, and taking away reproductive rights just makes people angry and less likely to reproduce.
This is true for more than 50% of the countries in the world, including UK, US, and Canada. And the trendlines are pointing down.
I spent 1.5 years working on this stuff in my last job. There are tons of reports out there from WHO, IMF, and the UN, all backing all this using fun terms like 'Demographic Time Bomb.'
tldr: We're screwed if we don't find a way to assimilate and encourage immigration, and reduce the cost of raising kids.
Thanks for coming to my TED talk.
Edit: Current government of Spain gets it: https://www.theguardian.com/world/2024/oct/09/pedro-sanchez-unveils-plans-to-make-it-easier-for-migrants-to-settle-in-spain