In The Narrowing Sea, Hannah Shepherd examines the shared histories of Pusan and Fukuoka over the eight decades from Japan's forced opening of Korea's ports in 1876 to the end of the Korean War in 1953. One city was Korean, the other Japanese; one was a burgeoning colonial port, the other a provincial city buoyed by imperial expansion. Wars, colonization, and capitalist industrialization forged intimate connections between the two, knitting together an imperial region that transcended its maritime boundaries. Drawing on both Japanese and Korean archives, and emphasizing the concept of imperial urbanization, Shepherd challenges traditional views of empire and urban growth and shows how local networks, migration, and capital flows shaped the region's exploitative and uneven geographies. The waters between Fukuoka and Pusan narrowed through intensified interactions that continued even after the end of empire, creating enduring legacies for the postwar and postcolonial eras.