Implementing International Law: The Worldwide Criminalization of Atrocities in Domestic Legal Systems, 1945-2010

Large bodies of research examine why states construct and ratify international legal agreements. Yet relatively little research assesses under what conditions states are likely to go further and implement, international law, that is, incorporate international legal rules into domestic laws – a step that is often crucial for making international legal agreements work as they are designed to. This study contributes to our understanding of why and when states make international law part of their domestic law by examining the patterns by which states worldwide have implemented one set of international legal norms, that is, criminal prohibitions against genocide, war crimes, and crimes against humanity. Since 1945, about three quarters of the world’s states have adopted a national criminal statue against at least one of these three categories of international crimes. In contrast to explanations for the spread of human rights norms that emphasize the role of bottom-up civil society advocacy, I argue that the implementation of such laws around the world over the past sixty years has largely been the result of choices made by technocratic legal experts who were appointed by governments to lead national criminal code reform projects. Though the desire to implement anti-atrocity norms has not motivated governments to initiate such reforms, these experts nonetheless used their delegated authority to codify norms – like anti-atrocity laws – that they believed embodied how a “modern” criminal code should look. Using event history and an original dataset covering the existence of national criminal laws against genocide, war crimes, and crimes against humanity in every country in the world that has adopted them since 1945, I find strong support for my argument that states that undertake wholesale redesigns of their criminal codes are highly likely to implement anti-atrocity laws, even while controlling for a variety of alternative explanations.