The development of social policy in East Asia has been gaining momentum in recent decades, challenging scholars to offer an explanation. This article addresses two questions: Are we witnessing the rise of welfare states in East Asia? And if so, what are the driving forces behind this development? We draw on theoretical perspectives of Franz-Xaver Kaufmann, who emphasizes the relationship between the state and civil society as the context of welfare statism, and who elaborated the role of international organizations and law in social policy ("welfare internationalism"). Choosing South Korea and Taiwan as examples, we explore the role of international policy diffusion, highlighting the interaction of international and domestic factors. We find that South Korea and Taiwan have indeed turned into welfare states, and that external "social" ideas, which have received little attention in previous research, have contributed to this development in different historical phases. Our analysis extends Kaufmann's perspective beyond Western welfare states.