In this episode of Our Human Nature, I discuss our plummeting global fertility rates, the incredible challenge this poses to nations, and the surprising connection between low birth rates and war. Around the globe, birth rates are falling below replacement rate. Our overall fertility rate has dropped in half since the 1960s. By the end of this century, only 6 nations are forecast to have enough births to sustain their economies. Apart from the incredible challenge this poses to nations, there is substantial evidence that depopulation prompts nations to become more territorially aggressive, accept higher risks, and seek expansionist policies, especially along shared international borders.