A topic common to the fields of early Korea and Mainland Southeast Asia is the transition from prehistory to early history. In both cases, imperialist scholarship of the early-to-mid twentieth century premised external civilizing forces of Sinicization and Indianization, respectively, as the sole explanatory mechanisms for the emergence of early states. With the subsequent development of autonomous archaeology, scholars now foreground local agency and indigenous development, and propose models of gradual change and interaction over sudden cultural or demic replacement. Key concepts include ‘protohistory’ as a distinct bridging period, and the ‘proto-state’ as a corresponding pre-state stage of social complexity. Crucial is that the proto-periods are present in the archaeological record. Examples in central MSEA include archaeology of protohistoric period formative to Pre-Angkorian era sites in the Lower Mekong system, and the notion of a proto-Dvāravatī period preceding the Dvāravatī polity of central Thailand. Both transitionary periods are dated to the 4th - 5th centuries CE. In Northeast Asia proto-history is a key concept for polities of the Korean peninsula. A ‘Proto-Three Kingdoms’ (1st - 3rd centuries) period was initially introduced to reconcile Chinese and transmitted peninsular sources, but its usage has expanded to state formation discourse of southern Korea. A notable parallel to MSEA is the southeastern region from which the state of Silla emerged with a protoperiod similarly spanning the 4th - 5th centuries. While in MSEA the structure of proto-polities are inferred from archaeology and early epigraphy, in Korea, the transmitted record, despite a distorted chronology, provides additional attestation for pre-state level social organization that is corroborated by early epigraphy. Comparisons of early Korea and MSEA provide us an opportunity to reflect on generic models of social development calibrated against regional specificities.