The objective of this study is to investigate inner motivation of Joseon dynasty for establishing rules of courtesy and rituals from the beginning as a vassal state, and the investigation starts from examining the process of establishing Joseon dynasty and how it differed from traditional way of abdicating the throne in China. The transition from Goryeo to Joseon dynasty is often referred to as a dynastic revolution, and yet, few studies have been undertaken on its definition or specific procedure. Even basic questions regarding the foundation of a country have been largely neglected including why founding members of Joseon dynasty started the new dynasty in the way they did, and what are their historical significance. In China, granting an imperial seal and crowning of a new king were essential rituals in the course of abdicating the throne. The ritual in China was different from how Joseon dynasty was founded. That is, the dynastic revolution of Joseon dynasty proceeded in a way different from a traditional Chinese way. The most important steps were altered or omitted. The giving and receiving of an imperial seal was entirely left out, and crowning was done by the queen dowager, but even the installed position was not that of a king. Why did founding members of Joseon dynasty undertake such incomplete revolution? The reason can be found in a long-standing practice during late Goryeo dynasty whereby the authenticity and legitimacy of a royal succession was decided by Mongolia. Such practice took root in consideration of Goryeo-Mongolian relationship, continued even after Joseon-Ming relation was newly formed, and eventually exerted influence on the dynastic revolution. As a result, crowning of Goryeo’s last king and an official ritual of giving and receiving an imperial seal were omitted. The dynastic revolution that founding members of Joseon dynasty undertook was meant to be completed by Ming dynasty’s crowning as had been customary at the time.