Lower birth rates are also happening in social-democratic European countries with extensive welfare states, social safety nets, and good upward mobility. It's not a uniquely American problem.

Meanwhile, families in war-torn African countries, people whose best aspirations in life are to own a flock of sheep and live on a farm, are having 6+ kids.

Low birth rates may be exacerbated at the moment by the economy, but people's preference for their careers and the quality and availability of modern entertainment (why raise kids when you can travel, binge watch shows on Netflix, play video games, etc.) are more probable causes.