Of the wide array of voluntary associations that either appeared or expanded their activities in Britain during the interwar period, by far the largest was the League of Nations Union (LNU). The result of a union between the First World War advocacy groups, the League of Nations Society, and the League of Free Nations Association, the LNU sought to mobilize support in Britain for the newly created League of Nations, the principle of collective security as the foundation of international affairs, and the ideal of internationalism itself as the best means of preventing war. The ways in which the LNU pursued these goals—public education campaigns, efforts to lobby press and Parliament, a subscription periodical—were not new, but the scale and scope of the LNU's activities far eclipsed that of earlier voluntary associations. Herein lies its historical significance, as McCarthy's fine book illustrates. The LNU was the most significant representation of the rise of liberal internationalism in postwar Britain, described by McCarthy as an expanded international and collectivist conception of the prewar ideas of arbitration, conciliation, and publicity. The LNU's success, measured by its impressive membership numbers (over 400,000, with branches throughout the United Kingdom at its peak in 1931) and the cross-party leadership it attracted (senior figures from Labour, the Conservatives, and the Liberals all appeared on the masthead of Headway, the LNU's journal), was due to its vision of internationalism as an adjunct to, rather than a replacement for, Britons' preexisting national, regional, political, class, and social identities. The LNU thus adopted a strategy of firmly centrist politics that allowed it to remain above the fray of party and class politics. This political malleability meant that membership in the LNU could reflect many motivations, from a commitment to the politics of internationalism to “the pleasures of sociability and the habits of association” (7). It was only in the late-1930s that the darkening international situation made such centrist politics untenable, and the LNU's embrace of the pacifist politics it had so long resisted necessarily meant it lost much of its previous support, and its cross-class coalition collapsed. Its post–Second World War successor, the United Nations Association, proved negligible.

McCarthy's book is not an institutional history of the LNU—Donald Birn's The League of Nations Union, 1918–1945 (Oxford, 1981) covers that material—but rather a study of how and why the LNU's positions on the league and internationalism resonated with the public in the interwar years. Her interest is in the “new diplomacy” of the postwar world, understood as the study, mobilization, and even transformation of public opinion for international aims. As what international relations scholars term a “norm entrepreneur,” the LNU helped establish internationalism as an important component of Britain's pluralist political culture. The most famous example was the LNU's famous Peace Ballot of 1935, whose success McCarthy persuasively shows was largely built upon the LNU's well-developed associational infrastructure. Despite the success of the Peace Ballot, the conduct of foreign relations remained in the hands of elites throughout the interwar period, and the general public proved uninterested in foreign questions much of the time, as McCarthy's use of press and public opinion data reveals. An expanded franchise, new international political space, and a growing voluntary sector, however, meant that even when the public did not make its views explicit, politicians and opinion leaders still paid it heed.

McCarthy develops her argument through a series of thematic chapters that show how the LNU secured its broad national base and then how and why it declined as a result of the broader collapse of centrism in the late 1930s. The LNU's politics were nonpartisan, epitomized by its leading figures, the “civic monks” Lord Robert Cecil (an aristocratic Tory, though of independent mind) and the classicist and Liberal Gilbert Murray. Its Christian internationalism allowed it to attract members from both Anglican and Free Church congregations, and it circulated internationalist educational materials widely. It mobilized the language and ritual imagery of nation and empire with the goal of creating “enlightened patriots” for whom internationalism was an extension of the familiar. The LNU's combination of paternalism and deliberative democracy enabled it to build a cross-class consensus that lasted into the mid-1930s, while its gendered recruiting messages were effective in penetrating the homosocial networks of interwar society. McCarthy's chapter on gendered internationalism is particularly strong, revealing the increased political opportunities available to women in the 1920s and 1930s.

McCarthy draws on a rich selection of source material. She makes use of expected sources such as the papers of Cecil and Murray, the LNU's main committee records, and government records. The book's real strength, however, is the detailed reading of branch committee and periodical evidence to build a nuanced sense of the LNU's public reach, especially outside of London. It would be interesting to know more about the LNU's cooperation and conflicts with other domestic voluntary associations, its contacts with other national pro-League organizations (all of which were smaller than the LNU and looked to it for leadership), and its positions on more of the League of Nations' struggles and successes. These are subjects, however, that go beyond the important question McCarthy has set for herself in this book: how did the LNU propagate a message of universalism in an age of fragmentation?