What did classical liberal thinkers contribute to the theoretical underpinnings of the European unification project? This paper examines works by Luigi Einaudi, Friedrich A. von Hayek and Wilhelm Röpke, attempting to understand to what extent the nineteenth-century pacifist tradition of classical liberalism came back to life in works of these authors. Their views on the international order show a certain degree of homogeneity—but up to a point. While Einaudi and Hayek were distinctively more favourable to the European project, Röpke had a less favourable view of European unificaton, fearing it may result in increasing centralisation. They, nonetheless, shared some common elements in understanding international order that we trace back to ni...