Clouds and VPSes

This is not a population bust in the biological boom/bust sense. These are caused by starvation or predator pressure. What we are seeing almost worldwide is the voluntary reduction of breeding rates in order to focus more resources on fewer offspring. This is largely because this is what women want, but also because there is an economic incentive: in poverty-stricken rural areas children become a source of free labour fairly fast as they grow up, so you can use one round of children to help fund the next, and having *lots* is to a certain degree beneficial to all of them. In cities they are and remain a substantial cost to the whole family, including any older children. So it's beneficial to have fewer.

(There is probably also something related to falling death rates: if you know that most of your children will survive, you'll have fewer. But the economic incentive is substantial even in the absence of that.)