Proto–Three Kingdoms period

The Proto–Three Kingdoms period (Korean: 원삼국시대; Hanja: 原三國時代) refers to the proto-historical period in the Korean Peninsula after the fall of Old Chosŏn and before the maturation of Goguryeo, Paekche, and Silla into full-fledged kingdoms. It is a subdivision of what is traditionally called Korea's Three Kingdoms period and covers the first three centuries of the Common Era, corresponding to the later phase of the Korean Iron Age.

Source: Wikipedia — Proto–Three Kingdoms period (CC BY-SA 4.0)