In grossly simplified terms, we might describe the historical periods so far considered in the following way. From 1815 to 1854 there was a stable distribution of power upon which the powers were able to base a successful concert; whereas from 1856 to 1914, while there may well have been periods of equilibrium, the powers were unable to operate a system in which concert principles played any significant part. From this perspective, the period 1918–39 represents a third distinctive form of ‘international order’ in the sense that its dominant feature was an attempt to operate a highly formalised and institutionalised concert system, namely the League of Nations, but, as there was a fundamental disequilibrium within the system, the conditions for concert were not present and the actual practice of states bore little resemblance to the concert principles formally enshrined in the League. In other words, the 1918–39 period may be viewed as having characteristics of both these former ages: like 1815–54 there was a collectivist aspiration and an attempt to introduce new diplomatic norms; like 1856–1914 the powers were thrown back upon their own individual resources and reverted, almost without exception, to traditional balance devices. We might say that as far as the ‘heart’ was concerned, the inter-war years shared the sentiments of concert diplomacy whilst the ‘head’ dictated a continuance of late-nineteenth-century balance strategies.