Since the founding, Goryeo Dynasty was constantly harassed by the invasion of the northern imperial dynasties. Joeson fought three wars with Gu Ran. In the ensuing war, even if Joeson made a peace agreement with Gum, it had to face a long period of war with Mongolia. But the conquest of Yeo Jin by Yun, Kwan indicates that Goryeo has not always taken a defensive position. As Yuan Dynasty declined, Goryeo’s King, Gongmin, strived to get away from the intervention of Yuan Dynasty and to win back the lost territory. However, due to the invasion of Honggunjeok and Japanese pirates, the dynasty fell into chaos. Eventually, Goryeo was overthrown by Lee, Sung Gae.