So, while the U.S. is not expected to shrink in population by 2100 (reaching 365.6 million), the largest age group will rise from 30-34 to 60-64 due to fewer young people having children.

New analysis from the World Population Review highlights which countries are the most at risk of a population decline, and Newsweek has compiled the data into a new map.

The United States has the third-largest population in the world, but nearly a third of the country's 340 million residents live in just three states, a new map reveals.