@Comrade Tovya.
Overpopulation isn't population density on its own, overpopulation is a state in which the land cannot provide the resources necessary to maintain the amount of life currently inhabating it.
The US has a lot more resources per square kilometre than any African country, therefore, it can sustain a lot more life per square kilometre, meaning that a greater population density in the US has less impact than one in the before mentioned African nation.
A good example of this is China and the UK. The UK has roughly 100 more people per square kilometre than PR China, however the UK has the resources to maintain life, moreso than PR China. When was the last time you heard of the UK government restricting births to one per couple?







