How borders are drawn and enforced has far-reaching consequences, whether we live on either side of them or halfway across the world.

Demographers have a name for when a population has more deaths than births: “Natural decrease.” It’s rarely discussed because “it is unusual in the modern era,” according to a recent research paper, but that’s about to change as natural decrease is becoming increasingly common across Europe, and in many parts of the United States.

In an article published in December’s issue of Population and Development Review, authors led by Kenneth Johnson of University of New Hampshire note that, “In Europe today there is virtually no overall population growth from natural increase.” There is only one country—Kosovo—with a population that is naturally growing by more than 1% per year.

By contrast, 17 European countries are experiencing natural decrease, including Russia, Germany and Italy. After analyzing census data from 2000 to 2010, the authors conclude:

“Deaths exceeded births in most counties of Germany, Hungary, Croatia, Romania, Bulgaria, and the Czech Republic, as well as in Sweden and the Baltic states. Farther south, natural decrease was also occurring in the majority of the counties of Greece, Portugal, and Italy.”

Natural decrease doesn’t mean a country is in danger of dying out completely, but it can create major economic difficulties. A declining population will tend to grow older, leaving fewer people in the workforce. As the proportion of old people rises, younger workers must pay a higher tax burden to pay for higher retirement, pension, and healthcare costs.

The map below shows population changes from 2000 to 2010, with blue indicating population increase and orange showing population decrease. White is a sign of missing data.

Population and Development Review. Source: Eurostat Overall natural increase or decrease, 2000-2010

Though the US had far fewer areas of natural decrease, there are still plenty. The authors found that 11% of US counties experienced natural decrease every year from 2000 to 2010, compared with 41% of counties in Europe.

Population and Development Review. Source: National Center for Health Statistics Natural decrease is far less common in the US than Europe.

But nearly half of US counties had at least one year of natural decrease from 2000-2010. After experiencing just one year of delcline, the authors note that it’s more than 90% likely to happen again.

“The likelihood of future subnational natural decrease is high in the US, just as it is in Europe,” they write.

The authors determine three major causes within the population for this decline: The percentage of people aged 65 or over, low fertility rates, and the proportion of women of childbearing age.

However they also identify a potential solution. The future of natural decrease is “not entirely bleak” in the US, they write, thanks to Hispanic immigrants, who are often of childbearing age and have high fertility rates.

Europe has received fewer immigrants in recent decades, though there has been a major increase in immigrants over the past few months. But the authors point out that it’s uncertain just how many immigrants will be accepted by which countries.

“Even if the immigrant surge is substantial, our analysis suggests that natural decrease is likely to remain widespread in Europe for the foreseeable future,” they write. In other words: “Natural decrease will certainly persist.”