ABSTRACT
This chapter focuses on the accomplishments of two major international relations (IR) traditions: one whose ultimate dependent variable is nation-state behaviour and one in which the understanding of such behaviour is an integral part of the explanation/ prediction of systemic outcomes. Kenneth Waltz operates with a systemic level, internal factors' level and a 'human' level for the purpose of explaining international conflict. Martin Hollis and Steve Smith suggest four levels: international system, nation state, bureaucracy and individual. The chapter explores the discussion of the unit/system cleavage in international politics to the theory of international politics by Waltz. Waltz sets out to explain units' behaviour and systemic outcome from 'structural' attributes of the international system as a whole. Post-bipolarity will make us aware, hopefully, of the seemingly enduring peculiarities of the international system in relation to other types of systems.
