> populations fall until the pressures causing suppressed reproduction ease
The problem is a falling population exacerbates those stresses. The economy crunches, anti-immigrant and right-wing forces gain power; the older population won’t vote to nix their benefits in favour of younger people, so either the system veers towards collapse or someone takes away their votes.
> Why would anti-immigrant voices gain power with a falling population?
I don’t think it’s a general rule. But the countries in a demographic bind are in one because they’re not getting immigrants. So as the vice tightens, we see those preëxisting tendencies amplified. This is more observational than prescriptive, mine you.
When the economy is crashing and more and more of society destabilizes, a huge amount of people will always look for politicians that will sell them "an easy way out". Being the politician that talks about inconvenient truths, the need for more immigrants, the need to keep high taxes as people are getting poorer and has a message of "hang in there" generally does not win people over.
Right wing anti-immigration parties sell an enemy (immigrants) as cause of all problems (they are stealing all our jobs!). In addition they sell tax breaks which also sound very appealing to people that struggle to get by on their current income. Of course all history shows that these "solutions" are lies, but history tend to repeat itself. The problem in a democracy is that the solutions that political parties present does not always have to be grounded in reality to be popular. Especially in these modern times with disinformation and conspiratorial thinking running rampant online (it's all Soros fault!).
The problem is a falling population exacerbates those stresses. The economy crunches, anti-immigrant and right-wing forces gain power; the older population won’t vote to nix their benefits in favour of younger people, so either the system veers towards collapse or someone takes away their votes.