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 so-cieties. 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 be-havior, this question takes on political salience. This paper seeks to de-scribe the phenomenon of constitutional incorporation of international law in greater detail and provide a preliminary empirical test of the com-peting 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 impli-cations 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.

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