A recurring debate in international politics centres on the distinction between peace and war. In recent years, this debate has resurfaced as a result of several developments, such as the Ukraine crisis and Chinese maritime activities in the South China Sea, which seem to blur the distinction. The Cold War confrontation between the United States and the Soviet Union made it clear that international relations could not be seen only through the lens of clearly separable cycles of peace and war. But the growing attention to the post-Cold War phenomenon of ‘hybrid warfare’ suggests that the line between peace and war simply cannot be drawn. This means that what constitutes war is destined to remain a contentious political matter. Yet it may be salutary that the contemporary strategic impulse to exploit this indeterminacy comes from the persistent fear of a general war, as it did during the Cold War. How this fear will evolve is key to envisioning the future of world politics and, in particular, its central uncertainty: whether the United States and China will go to war.