Unification is that groups formed based on common historical experiences and homogeneous cultures are divided and then combined into a single political body. The residents of the Three Kingdoms may not have recognized each other as the same nation, but it was already established as an objective entity and a group that became the original form of a nation. However, Silla implemented a policy of discrimination against the absorbed Baekje and Koguryeo residents. In addition, it was not able to inherit the wide-area diplomatic and cultural networks that Baekje and Koguryeo had. Therefore, Silla’s unification of the three kingdoms cannot be acknowledged, and in reality, Parhae claimed to be a successor to Koguryeo and developed a period of South and North states. Gungye contributed to the destruction of Silla’s traditional order, but failed to present any new ideology or policy to replace it. Gyeonhwon was a competent military commander and had an eye for foreign relations, so he engaged in diplomatic negotiations with various countries. However, there was no prospect of a new order, only an attitude to calm political and social confusion by reorganizing the existing governance system or using military power. On the other hand, Wang Geon tried to implement policies to solve structural problems, such as preferential treatment of strong local power and easing tax receipt of the people, and establish a Confucian political system. This goes beyond Silla’s antique o rder b ased o n Golpum system. In addition, it was not buried in the Chinese-centered worldview or cultural view, but emphasized traditional culture since the Three Kingdoms period. Parhae began to defect to Koryeo even before it was destroyed by the Liao Dynasty, and immediately after it was destroyed, a large number of royalty and nobles were absorbed into Koryeo. Therefore, it can be said that Wang Geon’s accomplishment is the first national unification in Korean history. Through the experience of the integration of the Three Kingdoms and the unification of the Later Three Kingdoms, we find that accurately recognizing the tasks faced by each era and trying to solve them led to the fruit of national unification. The reunification of the nation can be accelerated when sharing awareness of today’s fundamental problems, such as securing the right to live, social justice, and harmony between traditional and world cultures, and practicing them.