Commitment and Diffusion: Why 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 international law in the domestic legal order. In a global era, with an expanding 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 incorporation of international law in greater detail and provide a preliminary empirical test of the competing explanations for it. First, the discussion focuses on the concepts of monism and dualism, which have become conventional terms used by lawyers to describe the interaction of domestic and international legal systems. Second, a theory of commitments as well as the advantages and disadvantages of international 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 governments and state regimes, and bolster global reputations.