This demographic transformation caused by a rapidly aging population is new for the United States but not for other countries. Japan has the world’s oldest population, where more than one in four people are at least 65 years old. Already, its population has started to decline and, by 2050, it is projected to shrink by 20 million people.

Europe is headed down the same demographic path. Some countries in Western Europe have populations that are older than the U.S., notably Germany, Italy, France and Spain. Countries in Eastern Europe are even further along and, within a few years, many of their populations are projected to begin shrinking.

America has been different, until now.

Higher fertility and more international migration have helped stave off an aging population and the country has remained younger as a result. But those trends are changing. Americans are having fewer children and the baby boom of the 1950s and 1960s has yet to be repeated. Fewer babies, coupled with longer life expectancy equals a country that ages faster.