The final chapter discusses the possible existence of an omitted variable that could explain both the development paths followed by affluent countries in the interwar period and the intensity of revolutionary terrorism from 1970 to 2000. The level of individualism as an omitted variable is explored. "Individualism" here is defined as the autonomy of the individual vis-à-vis social groups, such as the family. The general hypothesis establishes that countries with a stronger tradition of individualism were better prepared for the introduction of capitalism and liberal democracy. Due to a greater elective affinity between cultural variables and economic and political developments, countries in which individualism was stronger underwent more peaceful modernization processes. The cross-national measurements of individualism are taken into account, showing a strong association with interwar development paths and revolutionary terrorism. In order to address the standard endogeneity objection, remote indicators of individualism (grammar rules and family rules of inheritance), which emanate from medieval times, are used as “instrumental variables.” The results are robust: The hypothesis on individualism is confirmed.