Over the past few decades, genocidal killing and other mass atrocities have become less frequent and less lethal. At the same time, collective international responses have become more common and more comprehensive. What explains these two phenomena, and are they connected? This article suggests that the evidence of declining mass violence and growing international activism is not only compelling but that the two phenomena are connected by the emergence of a new international human protection regime. The article proceeds in three parts. The first examines the evidence for thinking that the world is experiencing both a decline in mass violence and an increase in international activism in response to such violence. The second outlines the emergence, scope, and limits of the human protection regime. The third considers whether the regime itself is associated with the changing practices of third parties to mass violence. The fourth part contrasts this explanation with potential alternatives.
