ConflictLate 4th – early 3rd century BCE
Gojoseon versus Yan
Gojoseon’s rulers took the title of king and rivalled Yan, but early in the 3rd century BCE the Yan general Qin Kai seized some 2,000 li of its western lands.
Baomi · CC BY-SA 4.0 · Source
By the late 4th century BCE the ruler of Gojoseon called himself king and could challenge Yan. Under Kings Bu and Jun the throne passed from father to son, and offices such as minister and general appeared.
Qin Kai's invasion in the early 3rd century BCE cost Gojoseon its western territory, and its centre is thought to have shifted to the Taedong River.