Earlier quoted context omitted.
The drop in fertility rate is directly liked to migration into dense cities. They are just not a good place to have children. The US resisted the fertility drop for much longer, because of higher suburban population.
> The US resisted the fertility drop for much longer, because of higher suburban population. It was immigration, but next generation of all immigrants (native born) adopts host country total fertility rate in this context. https://www.pewresearch.org/short-reads/2019/08/08/hispanic-... https://www.pewresearch.org/short-reads/2016/10/26/5-facts-a... https://www.pewresearch.org/wp-content/uploads/2019/08/FT_19... visua…
It started falling to 1.6 around 2008 ( https://www.macrotrends.net/global-metrics/countries/usa/uni... ) which coincided with the millennials getting into the child-bearing age. And the millennials are much more likely to live in cities, even though they don't want that: https://news.gallup.com/poll/245249/americans-big-idea-livin...