Ketchup, you are right. I will agree, it was 9/11 that did that. Other countries did not have the baby boom central that USA did.
I think that people should have learned something from 9/11. New York is over populated. If all people had less kids, population would be lower and fewer people would die. In fact, if population was lower (I mean much lower), attack could have been prevented. Who would bother hitting a town if very few people are affected? It seems to me that evil often follows a crowded area, so they (evil shitbags) can harm more people at once.
In a sense of quality of living, I have to say that places with low population density do OK. Places with hight population density are really hard to make it in. Look at Mexico City for example. Crime, drugs, disease, human rights violations, corruption, so on. Look at a very small town in a USA (Exclude Indian reservations - not a good example). Maybe not the richest, but pretty survivable.