This chapter in the first place attempts to trace the incentives behind the early postwar integration of Europe. Apart from lessons learnt from the past, we show that European unity was pushed by some important context-dependent factors, like the specific distribution of power in post-1945 continental Western Europe. An analysis of the project’s uniqueness or unicity is followed by a section on its institutional and decision-making complexity—another striking characteristic of the European Union’s development. This study argues that the two were and are inextricably linked: The former (unicity) would not have been possible without the latter (complexity). Subsequently, we address the question of why some integration periods turned out to be successful and others not. Finally, the conclusion analyzes to what extent past incentives still hold relevance for the present. It will be argued that current Russian military aggression against Ukraine, combined with uncertainty about continuation of the US commitment to European security, has fundamentally changed the parameters of European integration and has made its course unpredictable. Nevertheless, seen from an historical perspective, as we have done in this chapter, the evolution is remarkable. The nation-state has not disappeared, but its place in the overall European development is certainly different from what it was at the beginning, in 1945.