The question whether and how warfare has influenced the development of advanced Western welfare states is contested. So far, scholarly work either focused on the trade-off between military and social spending or on case studies of individual countries. What is missing, however, is a systematic comparative approach that is informed by an explicit consideration of the underlying causal mechanisms. The aim of this lecture is to outline an agenda for a comparative analysis of the warfare -welfare state nexus. By distinguishing between three different phases (war preparation, warfare, and post-war period) it provides an overview of possible causal mechanisms linking war and the welfare state and provides preliminary empirical evidence for war waging, occupied and neutral countries in the age of mass warfare stretching from ca. the 1860s to the 1960s.