The post-Cold War era is placing the defense industry at a crossroads. If, on the one hand, it is under great pressure to guarantee warlike efforts around the world, with tight budgets and uncertain lead-times, on the other hand, it is seen as a central instrument for national sovereignty and foreign policy. The purpose of this research is to report the state-of-the-art of the existing literature and explore the most relevant research areas in order to provide the conceptual basis for further empirical research. To do so, this study uses a preferred reporting items for systematic review and meta-analysis (PRISMA), which is an adequate technique as it allows one to discover concepts, ideas, and debates about the defense industry. The results evidenced three different approaches to the defense industry—integration, autarky, and domination. In that regard, we present several case studies in which the defense industry is used as an instrument of foreign policy or national sovereignty. Future studies may focus on empirical research to validate the theoretical findings or to identify variables that lead some defense industries to seek synergies, resorting to mergers and acquisitions, while other defense companies prefer to obtain State funds.