Customary international law fills volumes of treatises, and we cannot try to show that all of it follows the logic of our models. Instead, we examine in detail four areas of customary international law chosen on the basis of their prominence and on the availability of a detailed historical record. The four case studies we examine are the “free ships, free goods” rule of wartime maritime commerce; the breadth of the territorial sea; ambassadorial immunity; and the wartime exemption from prize for coastal fishing vessels. We show that these areas of supposedly robust customary international law never reflected universal behavioral regularities and that the actual state behaviors associated with these laws are most easily and parsimoniously explained using our four models.
The customary international law of neutrality governs relations between neutrals and belligerents during times of war. One important neutrality issue is the status of enemy property on neutral ships. Before 1856, many belligerents, especially Britain, seized enemy property on neutrals’ ships. Conventional wisdom among courts and treatise writers holds that the principle of “free ships, free goods”—all property on a neutral’s ship, including enemy property but excluding contraband, is immune from seizure—became a well-established rule of customary international law after the Declaration of Paris in 1856 (Colombos and Higgins 1926, 164–67; Jessup 1928, 20–23; Moore 1906, 382; Woolsey 1901, 302–3). The Declaration followed the Crimean War, in which France,