If European integration is “the process whereby political actors in several distinct national settings are persuaded to shift their loyalties, expectations, and political activities toward a new center, whose institutions possess or demand jurisdiction over the pre-existing national states” (Ernst Haas, The Uniting of Europe: Political, Social, and Economic Forces, 1950–1957), then it has — as of yet — failed. While Europe's new center, Brussels, does indeed demand and execute jurisdiction in many areas, loyalties at least, have not fully shifted, or now shift even back to the nation state. Brexit provides us with the most spectacular example of how jurisdictions can quickly follow suit. Yet, common trends — either pro- or contra-integration — always have displayed significant cross-country variation and continue to do so. Religion is one of the major determinants of this variation, with Catholic voters, parties, and countries being on average substantially and stably more Euro-friendly than Protestant. This is the starting and ending observation of Religion and the Struggle for European Integration by Brent F. Nelsen and James L. Guth. The authors would be the last to be surprised that it is Protestant Britain which joined late and now is the first member state to abandon the “ever closer union” project.

To explain this very robust finding namely, Protestant skepticism and Catholic enthusiasm toward European integration, Nelsen and Guth in Part II of their book — after a conceptual, theoretical introduction of their core concept of “confessional cultures” — start with a very broad overview of Europe's religious heritage. In fact, Nelsen and Guth go back to the second and third century a.d., treating the Reformation and the Counter-Reformation, and then ending with describing the religious political movements that came out of the state-church conflict in the wake of 19th century's nation building process. Of course, nothing of this is really new, but Nelsen and Guth do a very fine job in providing the reader with a concise and informed overview of the longue durée of Europe's religious development, which proves to be of importance for understanding the diverse European confessional cultures that — so the authors claim — are behind the varying support for European integration.

Although Nelsen and Guth label their approach as “culturalist,” in Part III of their book on the formative phase of European integration in the early post-war years, they stress as probably the most important factor the stunning electoral success of Christian Democratic parties in post-war Europe. This appears to be quite a “hard-wired” mechanism of how the variable “share of Catholics in the population” translates into elites’ different political strategies. Again, much of what the authors describe has been described before, in works on Christian Democracy and the early phases of the European community. The value of the book is not that the authors present brand new evidence, but that they give a very useful and authoritative summary of the rich but dispersed literature, and that they synthesize these various pieces of literature into one very convincing argument, namely that the heritage of a Christian Europe and the conflictive historical relationship between the Catholic Church and the modern nation state contribute to the much more pronounced willingness of Catholic voters and Christian Democratic parties to overcome national boundaries in favor of a European community.

Rarely, however, the authors’ approach is in danger of repeating the weaknesses of the literature. For instance, with respect to the puzzle why all Christian Democratic parties but the French Mouvement Républicain Populaire (MRP) were electorally so successful in the first three post-war decades, the authors in line with the literature, offer basically a tautological “explanation”: “The MRP was less popular than its Christian Democratic partners precisely because it was unable to attract a unified Catholic voting bloc” (168). The MRP was unpopular because it was unsuccessful, and probably unsuccessful because it was unpopular. Also, the juxtaposition between a Catholic pro-European Union camp and a Protestant anti- European Union camp sometimes is confronted with a more complex reality, not only in the case of Irish and Polish reservations toward Brussels. (Nelsen and Guth address this on pages 291–294, but they could have explained it better with the fact that in these two cases, nation building did not take place against the Catholic Church, but with the help of the Catholic Church against Anglican Britain and Orthodox Russia (and Protestant Prussia) respectively (See David Martin's A General Theory of Secularization)). Consider also the German case: in the post-war struggles between a Francophile, Catholic, and pro-welfare wing versus the “transatlantic,” Protestant, and economically liberal wing inside the Christian Democratic Union, the Catholic “Adenauer camp” won all battles against the Protestant “Erhard camp,” but then the latter sought rescue from Europe, and succeeded to write into the treaty of Rome a liberal market order with relatively strict anti-cartel legislation, something they had not managed to do at home. So, the Protestant factor had not only been one of restraint, but shaped the very character of the center that wanted to become the new locus of political loyalties in Europe. This has some ironic, or should one say tragic consequences. For instance, when now in the Euro-crisis the Catholic south is forced to adjust to a “Northern” economic order. But of course, this example also supports Nelsen and Guth's claim: Europe's fault lines still follow confessional cultures and cleavages, even if West-European societies are very secularized today.

Nevertheless, these are minor, rather picky comments on a book that provides us with a broad, rich, and very convincing account on the impact of Europe's diverse religious heritages on today's integration project. Religion and the Struggle for European Integration surely is an important contribution to the literature.