The biggest issue facing the world is not the wars in Ukraine or Gaza, nor the prospect of great power war breaking out in the South China Sea. Climate change and food security are grave concerns and many fear that technological advances, particularly developments in artificial intelligence, will alter the future of work. But even those are not the main issues that will shape international politics into the future. Instead, the biggest issue facing humanity is its population—both the possibility that the human population will gradually wither away, and the ways in which shifts in population within countries and regions will affect international politics.
The global population reached 8 billion people in 2022, and is projected by the United Nations to reach just under 10 billion by 2050 and peak at just over 10 billion after 2080. At that point, the trend is expected to change. While precise projections are always challenging, the available evidence points to population growth slowing down and then eventually turning negative. The global population will shrink, likely before the end of this century.
The cause of this expected decline is not an existential event, such as nuclear war or a super virus killing off large segments of humanity. Instead, the cause of the expected population decline is more banal: Humans are simply not having as many children. As fertility rates in many parts of the world drop below the rate needed to replace the existing population, commonly set at 2.1 children per person who is able to give birth, global population will begin to decline. Even in countries and regions that presently have high fertility rates, those rates are lower than in the past.