Chapter 15 situates his work during the Cold War and the debate about convergence between the economic and political systems in the East and West. Tinbergen’s argument for coexistence of the two nuclear powers and economic systems is analyzed. This thesis of coexistence is later developed by Tinbergen into a theory of convergence, which is not rooted in economic or sociological theory, but is primarily a moral argument about the (search for an) optimal order. His idea of the optimal order is analyzed, in particular, to emphasize how deeply he had become an institutional thinker. The chapter also discusses various international interactions of Tinbergen in Indonesia, Spain, France, and elsewhere with military leaders and regimes to explore the consequences of his desire to always engage in conversation and to avoid conflict. These limits are further explored in a critique of his convergence thesis by his daughter and son-in-law. The chapter concludes with an analysis of an exchange between Oskar Morgenstern and Tinbergen about the role of the economist during the Cold War. Morgenstern worked for the US military to optimize military strategies, whereas Tinbergen argued that economists should direct their efforts to promoting peace.