The shift from Pro-fertility norms to Individual-choice norms followed by economic modernization reduces the extent to which people are willing to engage in war, contributing to the virtual disappearance of war between major powers. Cross-sectional evidence, longitudinal evidence and multi-level evidence from societies containing most of the world’s population indicates that rising existential security encourages a shift toward Individual-choice orientations and reduces tolerance of human casualties, bringing a diminishing willingness to fight for one’s country. These changes are closely related with the advent of knowledge societies which need a less hierarchical and a stereotypically feminine leadership style that emphasizes innovation and creativity. These findings echo the findings from recent works which suggests that “democratic peace” exists because most modern democracies are prosperous and interrelated through trade. The evidence suggests that this transformation has been going on over the last thirty years, strengthening the factors supporting international peace. While these trends are reversible, the norms of the Long Peace continue to prevail for now.