Please brother, don't make me imagine a world war with nukes. The whole world is going to collapse, It would take us atleast three century back and it would be the darkest chapter ever.
I think there are some really smart people in the world. We can use them to create beautiful discoveries. Seriously, it sends me shivers thinking of a world war, but it may happen, and I have no control over it. I have to just watch the world wither away.
Their population pyramid looks good though compared to China:
https://www.populationpyramid.net/united-states-of-america/2...
https://www.populationpyramid.net/united-states-of-america/2...
>how do you justify labelling a birth rate that's been below replacement for 18 years as "OK"?
The US being a nation of immigrants has this unique selling point of attracting people to make up for their woes such as birth rate. Unless we see millions of citizens getting deported, the people "voluntarily" relocating don't move the needle in this metric.