Now North Korea is faced with various kinds of crises, including economic, political and diplomatic ones. So it is highly possible sudden political changes could occur, which will bring about consecutive collapse of a state, a system and a regime in North Korea. Seemingly, such contingencies could take a form of coup d'etat, anarchy, civil war and the like. In those situations, South Korea should maintain peace and security on the Korean Peninsula more than anything else, and afterwards catch a chance of national unification in keeping pace with development of political situations in North Korea. Related to this, we must work out synthetic and systematic strategy for connecting North Korean contingencies to national unification of the two Koreas. International legal considerations and responses are most important in the preparation of unification strategies. Especially, international rules or norms such as self-determination, humanitarian intervention, de facto(or temporary) recognition of a de facto government, responsibility to protect(R2P), self-defence could be invoked during the course of integration of a divided state.