For at least half that time period between world wars, there was significant economic depression.
It might simply be the economy. The vibes are bad and have been bad since the late 70s because wealth distribution is lopsided and income growth is stagnant.
> It might simply be the economy. The vibes are bad and have been bad since the late 70s because wealth distribution is lopsided and income growth is stagnant.
Seems unlikely: the decrease in fertility rates is pretty universal, but what your are giving as reasons here seem pretty US specific.