This study investigates the relationship between external procurement of military capabilities and the outbreak of armed conflict between states. Researchers’ efforts in uncovering how and when governmental acquisition of military capabilities may precipitate violent confrontation, or rather inhibit fighting between states, have culminated in an array of research designs, theoretical arguments and mixed empirical evidence; thus contributing to contrary policy prescriptions. Scholarly work on the arms-war puzzle often misses that most governments depend on external parties for the acquisition of military capabilities. We argue that different armament transfer configurations lead arming states to evaluate war-related costs and outcomes differently. Cases where state dyads share a supplier of arms may induce a pacifying effect, as sharing partners can alleviate tensions that arise due to the uncertainty behind building capabilities, provide for peaceful conflict adjudication, and ultimately foster cooperation between states. But when state-dyads rely on distinct suppliers of arms, escalatory effects may be triggered if threat perceptions between suppliers and recipients of military capabilities reign. This argument is tested empirically, making use of data on Interwar armament transfers and statistical techniques that adequately control for network effects. The analysis shows that arming in itself is not a significant driver of conflict. Rather, the structures arising from cooperative or competitive behavior among recipients and suppliers of military capabilities condition the pacifying or escalatory effects of build-ups, respectively. In this way, this study proposes a novel argument and research design that extends the theoretical and empirical scope of previous scientific work.