We’ve already looked at how population rankings changed from 1939 to 2025.�Now let’s push the same list forward — all the way to 2100. Using UN World Population Prospects 2024, this is what happens to today’s 15 biggest countries if current demographic trends continue. 1. India stays on top, but the era of fast growth is over.�India remains #1 in 2100, yet barely grows. Fertility has fallen, the population is maturing, and size now comes from momentum, not expansion. 2. China’s decline reshapes