In this book Wolfram Kaiser, Professor of European Studies at the University of Portsmouth, ambitiously sets out to provide a revisionist approach to the history of post-1945 European integration, designed to correct what the author sees as the dominant state-centred paradigm of integration historiography. Kaiser’s revisionist intent appears to be twofold. First, ‘updating’ the writings of federalist historians like Walter Lipgens  and neo-functionalist social scientists like Ernst Haas  in the light of conceptual innovations in contemporary European Union studies , the author wants to bring "transnationally connected people and ideas back into the history of European integration" (p. 11). Second, the book is meant to contribute to overcome the isolated ‘niche’ status of integration historiography by connecting it "for the first time with the political and societal history of (western) Europe more generally" (p. 8). In the author’s view this also implies the need for a widening of the chronological framework: "This book demonstrates that any explanation of the origins of European Union after World War II needs to address the long-term continuities and change from the nineteenth century through to the postwar period." (p. 10)
Building on his previous work on political catholicism Kaiser chooses Christian democracy as the case study to exemplify his revisionist approach. The book tells the story of how transnational Christian democratic party networks and ideas – themselves reflecting the history of political catholicism since the late nineteenth century – have shaped European integration after 1945. The first four chapters chronologically reconstruct the history of Christian Democratic parties in Western Europe and the parallel emergence and development of their transnational networks up until the end of World War II. Chapter five depicts the rise of Christian Democracy to political hegemony in post-1945 Western Europe, while chapters six and seven attempt to demonstrate how the concomitant growth of the pan-European party network influenced the formative years of European integration until the Treaty of Rome. A final chapter takes the reader through to the 1990s, offering more selective evidence of a continued policy impact of the network despite the erosion of Christian Democracy’s hegemonic position in many countries.
Christian Democracy and the Origins of European Union is an impressive book in many respects. It is based on a vast range of archival sources from nine different countries. The painstaking reconstruction of the transnational party networks, rich in empirical detail, is in itself a major achievement. The chronological breadth is outstanding given that it does not come at the expense of historical contextualisation. And the book provides a good example of how political science approaches to European integration can be successfully appropriated by historians.
With regard to the twofold revisionist agenda Kaiser is most convincing in his insistence to bring transnational networks and ideas ‘back in’. Chapters six and seven supply evidence of how informal contacts and meetings between European Christian democrats had a decisive impact on specific moments of intergovernmental negotiations and domestic decision-making during the 1950s, perhaps most strikingly in the case of the rescue of the WEU Treaty in the French National Assembly in December 1954 (S. 277ff.). Still more importantly, Kaiser points to transnational Christian democratic ‘imprints’ on core ideas underlying the integration process during the first half of the 1950s. German-French reconciliation, for example, received powerful support by Christian Democrats’ transnationally shared (though flawed) notion of the "two Germanies": the "guilty Protestant-Prussian east", responsible for the rise of national socialism, and the "Catholic-Roman west, which could, and actually deserved to be, rehabilitated and integrated into the new Europe" (p. 215). The principle of supranationality, likewise, was strongly promoted by transnational Christian democracy against the backdrop of its parallels to the "quasi-supranational authority of the Pope" and the interpretation of European integration as a "democratic Carolingian Empire", whose perhaps most crucial task was to defend European civilisation against a "new Islam", the Communist Soviet Union (p. 228). The notion of "core Europe", too, had a Christian democratic "imprint" - Kaiser suggests that the non-participation of the UK was not only an act of self-exclusion, as Alan Milward has argued  but also reflected assumptions about cultural incompatibilities between Britain and the continent among Christian democratic leaders: "After all, Britain did not share the traditions of Catholicism and confessional politics." (p. 235)
While Kaiser’s focus on ideas and networks thus proves to have much potential for historiographical innovation it should be noted that his interpretation appears to complement rather than replace state-centred approaches. This is clearly demonstrated by the contrast between the ineffective transnational networking of the interwar period and the much greater influence after 1945, which was in large part due to the fact that Christian Democracy now became a major government party in many West European states.
Christian Democracy and the Origins of European Union yields mixed results with regard to its second major objective, the exemplary re-writing of integration history in the framework of a broader and longer-term European Gesellschaftsgeschichte. The author persuasively argues that we can not understand the outstanding commitment of Christian democratic parties to European integration after 1945 (in comparison to, for example, the socialists) without reference to the far-reaching transformation these parties underwent after World War II (e.g. endorsement of democracy and the welfare state, loosening of ties with Vatican). Kaiser also provides some indications about longer-term continuities conducive to integration, e.g. Catholic emphasis on regionalism and subsidiarity, yet overall his analysis suggests these were less important for the European ‘turn’ than the radical changes of the post-war period. This, in turn, raises the question whether the book’s extensive treatment of the pre-1945 history of political Catholicism is really as essential for the argument as the author suggests. In particular, the importance of pre-1945 transnational party networks for their post-war successors remains rather unclear. Kaiser admits that there were hardly any policy and institutional continuities between pre- and post-war networks (p. 186ff.) yet maintains that the interwar experiences "facilitated a collective learning process" and also implied a "growing realisation that political divisions could be more easily overcome with shared socio-economic objectives" (p. 117) – in analogy to the post-1945 functionalist integration logic. However, the author appears to be reading history backwards here – his later analysis of the post-1945 period makes very little reference to such ‘lessons’ of the past.
Christian Democracy and the Origins of European Union is not an easy book to read, and it is unfortunate that the author provides no conclusion to sum up and return to the more general issues raised in the introduction. All the same, Wolfram Kaiser’s book is a very important and innovative contribution to the field of European integration history.
 Walter Lipgens, Die Anfänge der europäischen Einigungspolitik 1945-1950, Teil 1: 1945-1947, Stuttgart 1977.
 Ernst B. Haas, The Uniting of Europe. Political, Social and Economic Forces 1950-57, Stanford 1958.
 Kaiser draws in particular on the political science literature on transnational networks and ‘governance’ - see for example Karen Heard-Lauréote, "Transnational Networks: Informal Governance in the European political space", in: Wolfram Kaiser, Peter Starie (eds.), Transnational European Union. Towards a common political space, London 2005, pp. 36-60.
 Alan S. Milward, The Rise and Fall of a national strategy. The UK and the European Community, vol 1: 1945-63, London 2002.