This introductory article sets out the key issues in the ‘unfinished business’ of East Asia’s twentieth century history. It argues that these are not limited to more well-known controversies around the legacy of Japanese colonialism and imperialism in East Asia, such as forced labour, war crimes, sexual slavery and the problem of collaborators. Rather, the unfinished business must also include the legacy of a postcolonial East Asia that was immediately thrown into the new maelstrom of the Cold War. This led to atrocities and still-unresolved historical issues on both sides of the Cold War divide, whether it be the suppression of dissent and brutal primitive accumulation of Stalinist industrialisation on the pro-Soviet side (China, North Korea) or the anti-communist massacres and crushing of opposition on the pro-US side (Taiwan, South Korea, Japan). This article further argues that a revival of critical Marxist historiography can contribute to a better understanding of the historical issues of twentieth century East Asia by stressing the social, political economic and geo-political dimensions that have frequently been neglected by nationalist historians and by the more recent turn to postcolonial and cultural history.