Who has the right to wage war? The answer to this question constitutes one of the most fundamental organizing principles of any international order. Under contemporary international humanitarian law, this right is essentially restricted to sovereign states. It has been conventionally assumed that this arrangement derives from the ideas of the late-sixteenth century jurist Alberico Gentili. Claire Vergerio argues that this story is a myth, invented in the late 1800s by a group of prominent international lawyers who crafted what would become the contemporary laws of war. These lawyers reinterpreted Gentili's writings on war after centuries of marginal interest, and this revival was deeply intertwined with a project of making the modern sovereign state the sole subject of international law. By uncovering the genesis and diffusion of this narrative, Vergerio calls for a profound reassessment of when and with what consequences war became the exclusive prerogative of sovereign states.