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.

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.