The key theme of this chapter is the second wave of institutionalisation of IR in the wake of the Second World War, and the onset of the nuclear era, the Cold War and decolonisation. Initially, the main focus of IR was again on the problems of the core as defined by the Cold War and nuclear weapons, reflected in theoretical developments, especially Realism and Neorealism, and Strategic Studies. Developments in liberal theories, such as Regional Integration Theory and Neoliberal Institutionalism, also focused on the problems of economic interdependence among the Western countries. The ‘great debate’ of this period, between scientific and classical approaches, did nothing to extend the purview of IR beyond the West. Despite the tentative beginnings of the dependencia perspective in the 1950s, it was only in the 1970s that concern with the Third World began to develop (along with IPE) as a main theme of IR. There was a massive widening and deepening of institutionalisation of the discipline, again most notably in the US and Britain, though also in Europe, Japan, Korea and others. There were a lot more research outfits, university chairs and departments devoted to the subject, and a lot more teaching of it. In the 1950s, the International Studies Association was founded in the USA and national academic IR associations formed and promoted the discipline in various ways.