Commitment and Diffusion: How and Why National Constitutions Incorporate International Law

Drafters of new constitutions face a bewildering array of choices as they seek to design stable and workable political institutions for their societies. One such set of choices concerns the status of interna- tional law in the domestic legal order. In a global era, with an ex- panding array of customary and treaty norms purporting to regulate formerly domestic behavior, this question takes on political salience. This paper seeks to describe the phenomenon of constitutional incor- poration of international law in greater detail and provide a prelimi- nary empirical test of the competing explanations for it. First, the dis- cussion focuses on the concepts of monism and dualism, which have become conventional terms used by lawyers to describe the interac- tion of domestic and international legal systems. Second, a theory of commitments as well as the advantages and disadvantages of interna- tional law are set forth. Third, empirical implications are developed for the precommitment and diffusion theories, which are then tested. Findings show that adopting international law is a useful strategy for democracies to lock in particular policies, encourage trust in govern- ments and state regimes, and bolster global reputations.