The First World War marked the formation of a brand-new European, as well as international order. In this historical context Ludwik Ehrlich proceeds to evaluate the foundations of liberal internationalism, to subsequently put down his conclusions in the 1918 paper entitled The War and Political Theory. The present article focuses on the development of Ehrlich’s thought, commencing with the issue of individualism from a psychological perspective, through the role of the state as a player in the international relations, the critique of the way 19th century German tradition construed the notion of sovereignty, and rounding it all up with the concept of psychological internationalism as the underlying principle of the new world order after World War I. With a view to ensuring a better appreciation of the way Ehrlich’s position was shaped, the Author assesses the impact of the war context and international academic debates pursued at the time on an individual human being, the state at large, and the very nature of international order.