There may be two P-Bombs: America, East Asia and Europe which spirals toward demographic collapse on one hand and Africa and - a bit less - the Islamic World which spirals toward overpopulation on the other hand.
E.g. Egypt which is already overpopulated fails to succeed to drive its fertility rate under 3. Maghreb countries such as Algeria and Morocco actually saw their fertility rates increase again after decreasing for the past decades. And that does even include demographic nightmares like Niger where half the population is systematically under 15