The history of European unity is not sexy. Historians have largely left it to political scientists, who in “historical innocence” (p. 2) have adopted rational choice models stressing nation-states' economic interests. Drawing on research in twenty-seven archives in eight countries, Wolfram Kaiser expertly fills this gap by integrating the origins of European unity into European history, in particular by documenting the links among transnationalism's leaders. That these individuals came overwhelmingly from Catholic milieux underscores the embeddedness of the European Union's origins in Christian democratic politics and ideologies. Kaiser's outstanding account demonstrates persuasively the Catholicity of European unity; in so doing, it reminds us of the salience of religious culture to twentieth-century European history.

Kaiser's survey impresses for its analytical incisiveness and chronological and geographic scope. He begins in the nineteenth century, where he identifies the roots of European unity in Catholics' embrace of subsidiarity and personalism in opposition to the centralized, liberal state. Taking advantage of the nineteenth-century upsurge in popular piety throughout Europe, Pope Pius IX worked to modernize European Catholicism. By imposing greater control over lower clergy and parishioners, asserting the Vatican's political agenda, and encouraging lay Catholics to battle anticlericalism, the pope laid the foundations for European integration. Catholic politicians did not initially pursue transnationalism for a number of reasons. While Catholics worked to defend their nationalist credentials and domestic religious freedoms, Catholic parties varied substantially in their organization and make-up. As Kaiser concludes, “Despite the transnationalisation of Catholicism as a religion and of the centralization of the Catholic Church as an institution, Catholic political parties thus remained quite nationally introspective until World War I” (p. 32).

Transnationalism took hold in interwar Europe for a number of reasons. Catholics' participation in WWI established their nationalist credentials; at the same time, shifts in papal policy, Catholic parties' expanded interest in such issues as workers' rights, and the founding of more pluralistic parties—including Italy's Italian Popular Party (PPI) and France's Popular Democratic Party (PDP)—created new political possibilities. Nevertheless, as Kaiser explains, the “window of opportunity for transnational party cooperation shortly after World War I was never more than half-open” (p. 54). While initial contacts, such as those between French and German parties, normalized transnational cooperation, the general decline of democracy across interwar Europe undermined transnationalism's overwhelmingly left-wing advocates. The marginalization of progressive Catholics even within the transnational movement was nowhere more evident than in the refusal of the International Association of Christian Inspired Democratic Parties (SIPDIC) to censure Italian fascism.

The displacement of these left-wing elites, who scattered into exile under fascism, by mainstream liberal and conservative Catholics as leaders of European unity marked a decisive shift in the history of integration. Politicians such as Konrad Adenauer would intensify prewar contacts and transnational efforts to lead postwar western Europe to unity. The political success of Christian democratic parties across western Europe positioned the movement as the primary motor behind European integration. Purged now of their antidemocratic elements, Christian democrats advanced a platform of continuity and change blending Catholic traditions, liberal economics, and strong welfare states. The impact of the Cold War, the decline of Catholic authoritarianism, a new sense of connectedness among Christian democratic parties, and the Vatican's embrace of Christian democracy all contributed to the realization of the European Coal and Steel Community and, in 1957, the European Economic Community. Strikingly, among most of its organizers, this Europe was imagined as a successor to the Carolingian, occidental Abendland excluding Britain. One of the great successes of the European unity project lay in persuading a younger generation of Protestant Europeans, both on the continent and in Britain, of transnationalism's legitimacy. Pervasive support for European unity would sustain the EEC beyond the 1960s, when the political hegemony of Christian democratic parties collapsed.

Kaiser offers a detailed yet extremely clear institutional history that effectively highlights the personal contacts and relationships among integration's supporters. While a book of nearly 400 pages with sixty-seven abbreviations should hardly be asked to do more, Kaiser's stress on long-term institutional continuity does risk obscuring the “ideational motivation” (p. 302) he argues drove European unity. Catholicism's ideological contributions to European unity and its organizational forms, such as a vision of a pre-Reformation Europe (Abendland), personalism, and subsidiarity, remain relatively underdeveloped here. Kaiser claims that Christian democrats “succeeded by their emotive appeal as much as by rational arguments at assimilating large sections of the younger generation of Christian democrats into their supranational policy consensus” (p. 321). Was that emotive appeal primarily the quest for peace and reconciliation after World War II? Prosperity? West Germans' desperate desire to rejoin the international community? A vision of an anti-materialist, hierarchical Catholic Europe?

It is in part the declining attractiveness of ideals of European unity that helps to explain the European Union's current troubles. Kaiser traces the history of European transnationalism through today, when the EU's weaknesses, demonstrated by the 2005 failed constitutional referenda in France and the Netherlands and the 2008 Irish rejection of the revised constitution, have many pondering its future. Kaiser's conclusion in this regard, however, seems apt: “Despite such recurring crises, which now frequently also affect democratic institutions and political parties in many member-states, the EU has proved—surprisingly for some—a durable legal-institutional supranational framework for the peaceful regulation of conflicts and decision-making on common policies. That its history should not attract the same attention as Hitler and Stalin owes much to the fact that it has not left the same deep tracks of blood across twentieth-century Europe” (p. 11).