'Why do war and political violence persist?' This simple yet tall question is what the author grapples with in this ambitious volume. He challenges the political realism paradigm according to which violent conflict is inherent to the international system. The book is centered on US national security and military policies – and the failures derived from its realist worldview. The ambition is to provide a synthesis of what peace research and security research can teach policy makers. The author suggests that the knowledge necessary to address these questions is available and just needs to be implemented. He proposes a new theoretical approach, an 'empirical realism'. Although it remains anchored in the initial premises of realism, the 'empirical' prefix emphasizes the importance of understanding the 'evidence' from state-of-the-art knowledge of global challenges. He identifies seven major transformations in the international system. Four challenge the current system, based on military power: the declining utility and increasing costs of war; rising influence and even threats from non-state actors; increasing non-military threats (e.g., environmental changes or cyberattacks); and growing nationalism. The three remaining transformations offer a more promising outlook, i.e., the growing realization that non-violent campaigns often have more impact than violent ones; the growth in communication tools, which, despite positive and negative outcomes, 'makes effective global governance an ever more realistic possibility' (p. 40); and the promise held by global governance if understood in new and imaginative ways. The main take home points from this useful review are that correlates of peace, rather than military power, should be maximized and that human security globally ultimately leads to more national security, even for the United States.