International law is a real phenomenon, but international law scholars exaggerate its power and significance. We have argued that the best explanation for when and why states comply with international law is not that states have internalized international law, or have a habit of complying with it, or are drawn by its moral pull, but simply that states act out of self-interest.
Part 1 argued that customary international law can reflect genuine cooperation or coordination, though only between pairs of states or among small groups of states. Other times, customary international law may reflect self-interested state behavior that, through coercion, produces gains for one state and losses for another. Much of customary international law is simply coincidence of interest.
Cooperation and coordination by custom have natural limits. We showed in part 2 how treaties can help overcome some of these limits. They do so by clarifying the nature of the moves that will count as cooperative actions in repeated prisoner’s dilemmas and as coordination in coordination games. Institutions associated with treaties—domestic ratification processes and the default rules of treaty interpretation—can also provide valuable information that promotes cooperation and coordination. Treaties can also reflect coercion and coincidence of interest, although in these contexts the presence of the treaty suggests that an apparent coercion or coincidence of interest situation has some cooperative element. Although treaties can foster cooperation and coordination more effectively than customary international law, there are still limits to what treaties can achieve—limits determined by the configuration of state interests, the distribution of state power, the logic of collective action, and asymmetric information. It follows that some