Chapter 4 shows how the appearance of Western whaling vessels off Japanese shores radically changed the archipelago’s geopolitical situation from the early 1820s. With the Shell-Repel edict of 1825, the shogunate reacted to informal offshore bartering and fears of uninvited foreign landings. The chapter outlines Atlantic and Japanese whaling histories, revealing that “traditional” Japanese whaling was in fact a substantial business that expanded rapidly over the seventeenth century, moving from shallow bays to the abundant Kuroshio ecosystem. For the Tokugawa shogunate, whaling was seen as a self-financing piece of defense infrastructure. Whalers were deployed against Russian incursions in Ezo in 1807, yet subsequent strategies centered on land-borne defense of strategic harbors. By the 1830s, geopolitical advisors to the shogunate worried about foreigners in the Bonins and proposed to incorporate the islands ahead of foreign navies. Due to political discord, an expedition was aborted in 1838. Only two years later, surviving castaways reported that the islands had become inhabited by people forth from foreign countries.

Chapter 1 observes that the Japanese archipelago has been represented unduly as an “islanded” entity, due to the prevalence of exceptionalist concepts such as national seclusion or sakoku. It presents Japan as a terraqueous economy by outlining the history of marine nutrients from fishing grounds along the Kuroshio and Oyashio currents, which remained prominent factors in the expansion of agrarian production until the twentieth century. It suggests different possibilities to embed the archipelago’s early modern and modern histories conceptually in its hydrological environments: Teleconnections such as the East Asian Monsoon offer historiographical challenges to Eurocentric models like the “East Asian Mediterranean.” Likewise, maritime currents are agents in the making and remaking of Japan’s terraqueous economy. Their seasonal rhythms create specific environments of risk in which the archipelago’s marine resource and shipping industries developed their business practices. The Kuroshio offers special possibilities, because it represents both a modern scientific concept and an early modern source term – its study can therefore build on intellectual and vernacular virtual geographies.

Chapter 2 offers a case study centered on the island of Hachijō, where life with the current gave rise to unique economic practices and social organization. It centers on the seasonal rhythm of castaway arrivals and repatriation that, by the mid-eighteenth century, had become an important branch of the local economy. Numbers of castaways were significant because sailors used winds and the eastward current to propel their voyage, even though their crafts were unfit for offshore sailing. In the peak year of 1850 alone, 300 sailors arrived on twenty-seven vessels from western Japan. Historical arrivals of foreign castaways and flotsam have created a virtual geography and local identity that connected the remote island to India, whence the “river” Kuroshio was believed to flow, and China, whence the current was believed to have brought important cultural achievements.

The introduction points out that changing human presence in the Pacific affected Japanese politics throughout the nineteenth century. In particular, the whaling boom of the 1820s to 1840s caused security anxieties among policymakers, while Japanese whalers by mid-century struggled with declining catch rates. Building on scholarship from Oceania, the introduction suggests thinking of Japan not as an island, but as a “Sea of Islands,” a terraqueous zone awash in currents such as the Kuroshio south of Honshu that allocate warmth, humidity, and nutrients and create a specific, though fluid, offshore geography in which consequential historical conflicts and competitions unfold. It lays out a set of questions that emerge from such framing and suggests conceptualizing the history of the Kuroshio’s catchment area as an oceanic frontier. This brings the historical significance of ocean, islands, and human travelers beyond the traditional human habitat to the fore. Since the seventeenth century, ongoing attempts at controlling this frontier has informed business practices and expansionist ideologies of Japan.

Chapter 3 argues that Tokugawa Japan exerted an important influence on the way global geographers mapped and conceptualized what is known today as “the Pacific.” It shows how the ocean has been the object of diverging metageographical categorizations in different cultural and political contexts in Japan, Asia, and Oceania. Over the Tokugawa period, its meanings changed radically in Japan. In fact, even decades after the issue of maritime prohibitions, in 1675, the Tokugawa shogunate successfully explored and mapped the then-uninhabited Bonin Islands. For Japanese intellectuals, the subsequent “discovery” of the Pacific coincided with an intellectual emancipation from the continent, as Hayashi Shihei’s late-eighteenth century works illustrate. Concepts and geographical data created in the process were highly classified, yet they were among the first Japanese texts to be translated in Europe in the early nineteenth century, where they entered globalizing geographical discourses. Like the malleable category of Nan’yō or “the South Sea,” some metageographical categories remained politically distinct until the twentieth century.

Chapter 8 observes the emergence of frontier tycoons toward the close of the nineteenth century, carried by a wave of “South Sea Romanticism” in literature and politics, propagated publicly by a pathos of drift and discovery. Fueled by insurgent demands of popular rights in the 1870s, grassroots expansionists claimed a “national right” to adventure and opportunity in the ocean frontier. Petty entrepreneurs of questionable reputation and ambivalent attitudes towards the law “opened” remote isles where state control faded. Others, like the entrepreneur Koga Tatsushirō who appropriated the Senkaku (Diaoyu) islands in 1895, enjoyed governmental backing. Such island colonies were eventually absorbed by the empire’s corporate infrastructure and were refashioned as sandboxes for colonial administration. “Rogue entrepreneurs” meanwhile traveled as far as the Caroline Islands in Micronesia, where one businessman, operating below the government’s radar, eventually facilitated the installation of a Japanese South Seas Protectorate. The chapter argues that the Japanese empire’s modalities of expansion carried the imprint of these experiences.

Chapter 5 discusses how intensifying transpacific traffic along the Kuroshio affected Japan’s geopolitical situation in the mid nineteenth century. It argues that the so-called “opening” of Japan was a process that began at sea and crept ashore in peripheral locations such as the Yaeyama Islands of Ryukyu, where a mutiny on a “coolie” ship involved local authorities in a violent, international conflict. For decades, Japanese governments had been coping with naval incursions and weighed different strategies for defense reforms, though domestic controversies delayed these efforts. By 1853, the American quest for steam-powered access attracted new interest to land-borne coaling infrastructure across the Japanese archipelago, a pursuit that materialized with Commodore Perry’s expedition to Japan, Ryukyu, and the Bonin Islands. The chapter shows how the shogunate and Japanese domains competed to reverse engineer steam engines and sailing technologies, and eventually to deploy their own steam-powered facilities to reclaim the strategically located Bonin Islands.