During the High-Level Talks period (1990-1992), the two Koreas showed their “good faith” to end antagonism and build the foundations of peaceful coexistence and ease tension. There was no real willingness to accept the other party’s position and no real agreements were reached at all. As a result, the High-Level talks and other related efforts to achieve greater inter-Korean cooperation were bound to fail: they were never going to move the reunification process forward significantly. This notion runs counter to conventional notions of neofunctionalism that cooperation in functional and non-contentious fields can spillover to produce greater cooperation in other, more contentious fields. Both Koreas made efforts to increase cooperation through the Basic Agreement as a sign of creating institutional agreements. This cooperation can be explained by the propositions relating to institutionalization that are developed in neofunctionalism. Both Koreas’ perception of mutual benefits was a major factor which encouraged cooperation in a situation where each side had ruled out the use of armed aggression. I argue that these perceptions can be explained by the propositions relating to absolute gains concerns that are developed in neoliberal theory. In contrast, both sides’ concerns about the relative losses from inter-Korean cooperation gave rise to security fears. The breakdown of cooperation can be analyzed using the propositions about relative gains concerns as non-cooperation developed in neorealist theory. The emergence of the possible use of armed aggression was a key factor for the failure of the two Koreas to maintain cooperation. In conclusion, each of three ‘orthodox’ theories has a partial relevance in explaining the symptoms of cooperation and the revival of the antagonism between North and South Korea even though they are neither theories of reunification nor primarily concerned with explaining the politics and economics of Northeast Asia.