[jrochkind1]

If we need more young people in our society in the USA, this is actually the easiest problem to solve -- just open up immigration. As long as lots of people still want to come here (not guaranteed to last forever), not having enough people is a problem only of our own making. If only most of our problems were so easy to solve.

[pelzatessa]

It's only a short term solution, as all countries around the world (even those third-world ones, with current fertility rate above 4.0) are experiencing lower birthrates every year. See the movie birthgap

[jrochkind1]

As long as people from those countries want to come to the USA, it would be a problem for those countries and not the USA.

However, "those third-world ones with current fertility rates above 4.0" probably have a ways to drop before it actually becomes a problem for them, couple few generations or so. In that time, the context for all of this could change (50 years ago, people were more worried about too much reproduction? Who knows in another 50).

In fact, for whatever reasons, the most predictable trend seems to be that fertility rates are inversely correlated with standard of living. As standard of living goes up, fertility goes down and vice versa. if those "third world ones" actually drop their fertility to "first world" levels, it would probably mean that their standard of living is such that immigration to the USA won't be so appealing either.

At that point, it seems the global social political context is changed enough that we will have an entirely different set of problems and solutions that are hard to predict now.