During the late nineteenth and early twentieth centuries, the world’s territory was carved into a handful of colonial empires. With few exceptions, the so-called ‘new imperialism’ of these years incorporated states into the world system either as colonizers or colonized. Japan’s case was unusual: the country started out as a victim of imperialism in the nineteenth century, but became an aggressor in the twentieth. Accounts of Japan’s empire have often fixated on the peculiarities of a non-Western, late-developing imperial power—what one of the architects of the field of Japanese colonial studies called ‘an anomaly of modern history’. The inter-connections between Japanese imperialism in mainland East Asia, the conclusion of the Chinese civil war, and heightened Cold War friction in the immediate post-Second World War period are re-examined here as distinct regional dynamics for the end of one empire and the rise of others in the 1940s and beyond.