Political scientists have in recent years produced many illuminating and enjoyable studies of historical subjects, including James C. Scott's Against the grain: a deep history of the earliest states (New Haven 2017) and Ayşe Zarakol, Before the West: the rise and fall of eastern world orders (Cambridge 2022). The political scientists’ commitment to explain what is going on and why it matters to audiences who cannot reliably tell their khans from their kings of kings makes them excellent guides to unfamiliar topics that also stimulate historians to show the wider relevance of what we do. This book, unfortunately, falls short of this standard.

Bruce Bueno de Mesquita is a professor of politics with a particular interest in game theory. In this book he proposes to explain the rise of ‘western exceptionalism’ as the result of the agreements reached between the papacy and the Holy Roman Emperor at the Concordat of Worms (1122) and the similar treaties with the kings of France and England. The rules for how to appoint bishops agreed here, and the regulated competition that followed, it is alleged, set these parts of Europe on a path to exceptionalism. The results can still be read today in the wealth, health and well-functioning democratic systems of the countries once covered by the concordats and their ‘settler offshoots’ (p. 254). Chapters i and ii lay out the background, chapter iii explains the nature of the ‘concordat game’ between Church and Crown, while chapters iv–viii set out its consequences, culminating in a series of recommendations for modern day governments that wish to share in the fruits of the concordat (free, regulated competition, freedom of religion, but no religious influence on politics). This is backed up by numerous anecdotes and, more importantly, a wealth of graphs showing the ebb and flow of secular and religious influence and the economic developments of particular dioceses and countries.

There are many ways in which quantitative approaches to the bewildering complexity of medieval evidence can be helpful. But it really will not do to dismiss the challenges involved with the comment that ‘[n]aturally, any such measurement can only be imperfect’, before then proceeding to plot a graph of papal power by analysing ‘the images of European art found in the leading contemporary art history text books’ (p. 54). The footnote identifies the five books in question. The author explains: ‘I assume the authors did not choose what to include based on anything like the thesis I have put forth; rather, I assume they sought to depict the important, influential images’ of the relevant period and place. The assumption that art history textbooks can be used as neutral samplers of the art of the time is dubious: how does the author propose to compensate for the need for variety in text books, that will inevitably mean that, for instance, relatively few of the many presentations of Christ in his majesty that we find in medieval manuscripts make it into the hands of students? How do we distinguish between ‘secular’ and ‘Christian’ art in a period where the political and religious imagery were so closely linked? The footnote explains that the author ‘asked art history students to code the images of European art’ from the four texts, ‘based on whether the primary subject matter was Christian … or non-Christian’. This sounds like a fun class exercise, but to make it into a graph and then use it to chart papal influence over Europe is dubious, at best.

The charts of secular versus religious art are, however, only a small part of the argument; more worrying is it that the evidence for the central question of backgrounds of appointed bishops (were they former royal officials or ‘religiously oriented’) has been assembled in a similar manner, namely by ‘scraping Catholic Church websites and Wikipedia sites’ (p. 302). This is a very offhand way of assembling critical pieces of evidence and severely undermines the reliability of the results.

The core of the book's argument is in the author's presentation of ‘the concordat game’ in chapter iii. Briefly summarised, the concordat gives the Church the right to present candidates to a bishopric, and the monarch power to refuse or accept them, If the monarch refuses, they keep the income from the bishopric until a bishop is appointed. The Church favours ‘religiously-oriented’ bishops, while monarchs favour the ‘secularly-oriented’. The logic of the concordat game would make the Church (or pope; the two are, intentionally, conflated, to make the game theory setup simpler) propose religious bishops in poor bishoprics (where the monarch is unlikely to want to risk the cost of papal anger) and worldly bishops in rich bishoprics (where the monarch would not accept a religiously-oriented candidate). Sensible enough, and the percentages that the author presents seems to suggest that was indeed how things unfolded: ‘wealthy sees had approximately twice the odds of getting a secularly-aligned bishop as did poor bishoprics’ (p. 114).

The problems begin to arise when we get to the conclusions that the author draws from the ‘concordat game’ which, he alleges, set the framework, not just for interactions between Church and monarchy but more generally for both institutions’ attitude to society: ‘Whereas the preconcordat environment provided no special incentives to promote – or hinder economic productivity and development … [k]ings now had a reason to stimulate economic growth as the pathway to greater political control over their territory. Popes now had a reason to limit economic growth’ (p. 89). This had ‘profound consequences’ leading not only to the economic miracle of the twelfth century (albeit with caveats at p. 158) and the ‘creation of parliaments – as a way to incentivise a work ethic that motivated the effort needed to generate wealth’ (pp. 90–1), but ultimately to the rise of the West.

There are obvious caveats to be made here – surely kings had other reasons to promote economic growth (before and after 1122) than simply its influence on the appointment of bishops? Surely local bishops had reason to stimulate economic growth, no matter the interest of the pope? But more importantly, the author's conclusion fails, even measured according to its own logic. The distinction between rich and poor dioceses is always, necessarily, relative. Since it's impossible to put a fixed cost on being excommunicated, the question of whether you want to risk it in order to appoint your pal archbishop of Canterbury must (in game theory terms) depend on how big a slice of your income and influence said archbishop represents. Therefore, the ‘concordat game’ would not change popes or kings’ general interest in economic growth.

The most serious problem with this book, however, is not in the way it treats the European material which is, at least, sympathetic, but how it engages with the rest of the world. Which is to say, barely. We are told on p. 24 that the core cause for Europe's exceptionalism is ‘this surprisingly simple reason: in Europe the head of religion and the head(s) of state were different people’ engaged in long-standing conflict. The only concrete example we are given of the situation outside Europe is Ghenghis Khan's lawcode, the Yassa, that asserted the khan's absolute power. That Ghenghis Khan is viewed as exemplary of the situation outside Europe suggests that not enough work has gone into looking at what was actually happening here. The author's fellow political scientist, Zarakol, points out that Asia prior to the thirteenth-century Mongolian conquests had a distribution of legislative, ideological and political power that is not too far from what we know in Europe: Chinese emperors had to share with the Confucian civil service elite, Islamic sultans with both the kaliph and experts in Islamic law. The question of why Europe came to show such striking dynamism in the early modern/modern period remains critically important, but we cannot hope to answer it without more fine-grained comparison and an awareness that things changed, outside Europe too.

The book raises an important problem: how should medievalists engage with the increasing number of political scientists who are showing an interest in our period? They are going to keep coming, and they command a language and form of analysis and presentation that makes their work much more accessible to policy-makers, and to many members of the wider public. To simply shake our heads and ignore them would be, like this book, a wasted opportunity; we must try to engage with them, learn from them and guide them through the treacherous jungles of medieval evidence.