Most of the world has experienced a revolutionary and unprecedented development over the course of the last century and especially since the end of the Second World War: significant population aging. By any standard measure—median age, the number of 60- or 65-year-olds and over as a percentage of a population, or old-age dependency ratios (the ratio of seniors to working-age adults), most of the world is significantly older today than in the middle of the 20th century, and the trend is accelerating.
The world’s great powers have not been immune to this trend. To the contrary, many of these countries have been leading the way, aging faster and to a greater extent than most other countries. By 2050, the median age of China, France, Germany, Japan, Russia, the United Kingdom, and the United States will be at least 40. Germany and Japan are currently two of the oldest countries in the world, and China is likely aging faster than any other country in history.
How is the near worldwide phenomenon of population aging likely to affect international relations (IR)? Most scholars who have examined this issue have linked the potential effects created by aging to established IR theories. Most analyses that have developed around the issue of aging, in other words, have not created new theoretical approaches to the study of international politics. They have instead argued that aging is likely to affect key variables associated with existing IR theories, which will then tend to generate particular outcomes based on these theories’ predictions. The IR theories that studies of populating aging have most frequently tied into include ones from realist, diversionary war, and constructivist research programs. Many of the arguments that link the effects of aging to these theories reach opposite conclusions, with some predicting a much higher probability of international conflict due to aging, others the reverse. There are, however, very few empirical analyses that test these competing hypotheses, largely because aging is such a new phenomenon.