Defence cooperation between Western European countries has increased considerably since the end of the Cold War. An analytical distinction can be made between political and economic cooperation, the latter having been neglected by political scientists. This study advances the debate on economic cooperation by identifying sources of variation in the European Union (EU)-15 countries’ membership rate in cooperative armaments fora aimed at restructuring the demand side of European defence from 1996 to 2006. By combining six models from three different schools of thought, the risk of confirmation bias through intra-paradigmatic reasoning is reduced. At the same time, fuzzy-set analysis opens up the space for data-driven combination effects. Two distinct combinations form sufficient paths leading to high rates of membership. Most importantly, intentions to create collective defence technological and industrial benefits combine with trust in partners’ ability and integrity to form an essential combination of conditions for governments to pursue cooperation on armaments.
