The Vicious Cycle between Demography and War

This paper highlights a vicious circle between demography and war. Countries face the choice between two possible equilibria. The first equilibrium is characterized by high fertility rates, a predominantly young population with a low median age, and a high risk of conflict. In contrast, the second equilibrium is marked by low fertility rates, higher life expectancy, an aging population, and no youth bulge which increase the probability of conflict and war. The data emphasize that countries with high fertility rates, above five children per woman, face a 75% likelihood of experiencing conflict. In contrast, countries with fertility rates below two exhibit less than an 8% probability of conflict. This paper presents a new framework in which fertility rates and the probability of conflict are endogenously determined, leading to multiple equilibrium outcomes. The core idea is that high fertility rates increase the likelihood of conflict due to the "youth bulge" phenomenon. Conversely, war and conflict—by causing high mortality among soldiers—motivate families to increase their birth rates. This reciprocal dynamic results in multiple possible equilibria. As a result, the world faces regional disparities in conflict and population growth. On the one hand, there are countries characterized by low fertility rates, an aging population, and high capital stock, which experience low conflict probabilities. In contrast, there are regions such as parts of Africa and the Middle East, with high fertility rates and younger populations, which are more prone to conflict.