I’m going to guess Nigeria - https://www.populationpyramid.net/nigeria/2017/
Nigeria’s trend is to double its population to almost 400M by 2050, and close to 1B by 2100.
By contrast, India’s population growth seems to be levelling off. https://www.populationpyramid.net/india/2017/
Asia as a whole is about 4.5B and projected to peak at 5B
For comparisons, check Russia and Japan on that website. Most developed countries are heading for a levelling and serious decline in population. This is a side-effect of a society where children are less of a financial asset and more of a burden; plus women’s lib allows women to have a greater say in reproduction.
But current world population is pushing 8 billion and projections (that website) say 10 billion by the end of the century. Where will all those people go? Even India and Indonesia are levelling off. Only the African continent seems to be into uncontrolled growth. What’s its carrying capacity? Will they have the money to institute a green revolution to feed that many people? perhaps we’re seeing the initial side-effects of this problem in the Mediterranean lately.
As the saying goes: “If things can’t keep going on this way - they won’t.”
OTOH, what’s the projection for climate change? A limiting factor in Africa is that there is no water, agriculture can be marginal in most areas. Almost all the rainfall occurs in a matter of two months. Will climate change mean a wetter Africa and India, or a drier one?
Finally, for human action culls, rather than relying on Mother Nature - the problem with the world is that nobody’s in charge. Therefore, the most likely action will be each country thinking - the neighbours are a pest, and have nice land. What can we do to expand that-a-way? An alternative is action at a distance, where North America or China concludes the tropical jungle areas far to the south would better help the climate recover if they were deserted jungles. It’s the mechanism that’s the problem - disease always risks coming home to roost. Causing crop failure means floods of desperate people washing up on your shores. Perhaps some sort of mass sterilization would be effective with less disruption (Handmaid’s Tale, anyone?), but again - how? Any biological warfare has the boomerang factor, plus retaliation. Maybe embargo the country from modern supplies like oil and gas - but that requires the whole world to gang up on someone. North Korea has demonstrated that’s easier said than done.
Finally, there’s the moral factor. The gas chambers were allegedly developed by the Nazis because there were complaints from the regular troops that they signed up to fight for the fatherland, not to shoot women an children into mass graves as the marched across eastern Europe. You know that in regimented troops in authoritarian Germany the complaints must have been pretty loud for the high command to sit up and notice. Even then, they did not tell their general public what they were up to. I cannot imagine any advanced country making it an official policy that they were going to murder every man, woman and child in a particular ethnic group or neighbouring country, and not facing internal and external objections.
it would certainly have to be a very different time.