The main purpose of this thesis is to explore the complex relations between South Korea's national security, state identity, and engagement policy towards North Korea over the years, with the primary temporal focus on the Kim Dae Jung administration (1998-2003) and in terms of the conventional and critical constructivism in International Relations (IR). Related to the South's engagement with the North, this thesis also aims to critically examine Pyongyang's Korean nationalism and National Cooperation (Minjok Gongjo) Doctrine directed at South Korea (and even the United States) at the dawn of the 21 century. Before embarking on the above empirical analyses, the thesis theoretically considers constructivist security studies as an analytical framework for examining Korea's identity politics during the Kim Dae Jung administration. The thesis also considers the historical context of South Korea's national security until the late 1990s, just before the advent of the Kim Dae Jung administration in 1998.