Anna M. Grzymala-Busse's impressive new book convincingly places the Catholic Church at the center of pre-modern Europe's divergent road to state formation, in two ways. First, the Church pioneered administrative techniques and practices that spread to and transformed Europe's secular states. Second, it deliberately fostered a competitive interstate system that fueled the incessant warfare singled out as key by other accounts of Europe's development.

According to Grzymała-Busse, the Church contributed to administrative and political development in several ways. It introduced new institutional models for taxation, petitions, courts, and parliaments that were emulated by European lay rulers. Clerical scholars were also essential in developing and spreading the use of Roman and canon law. Furthermore, the increased need for legal expertise fueled the expansion of educational opportunities, in the form of medieval universities. Without the Catholic Church the templates for administrative and political apparatus of European states would have been much more limited. The consequence would have been less centralized and effective tax collection, lower levels of representation, a higher frequency of feuds and use of blood money to settle disputes, and lower levels of human capital formation. Ironically enough, these state capacities later allowed secular states to make the Church subservient to state power.

The Catholic Church also played a more direct role in European state formation. The machinations of successive medieval popes fostered the geopolitical fragmentation of Europe as popes sought to free the Church from the clutches of secular rulers. Contrary to existing analyses, Grzymała-Busse thus finds that papal-led conflict is correlated with increased territorial fragmentation and urban self-government during the medieval period, while secular conflict is positively related to political fragmentation only in the early modern period. War, and papal-led war, in particular, was what allowed small states and autonomous cities to survive well into the early modern period.

Sacred Foundations is a compelling read that presents a bold new take on European state formation. The book marshals an impressive amount of evidence, presenting new data on excommunications, religious conflict, monasteries, and the adoption of new state institutions among other things, to support its claims about the many ways that the Catholic Church placed European states on a new path. In addition, the book's thorough grounding in historical work is commendable.

The book's main weakness—if one can call it that—flows from its broad ambitions. In examining the myriad of influences that the Church had on European state formation, it sometimes leaves the reader wanting a more thorough empirical examination of the specific arguments. To give an example: When analyzing the effects of papal versus secular conflict on territorial fragmentation and the emergence of communes in Chapter 2, the findings are based on a two-way fixed effects approach. These results rely on the ability to reliably code and distinguish papal conflicts from secular conflicts. This is potentially problematic as the underlying databases used to code secular and papal conflicts are not the same, and as a result, the criteria for defining a conflict may differ. Based on the more extensive discussion of these variables in the accompanying article (“Tilly Goes to Church: The Religious and Medieval Roots of European State Fragmentation.” American Political Science Review, published online [2023]), the papal conflict variable seems to code a bigger variety of instances as conflict, including, for instance, papal depositions. Therefore, the analysis might be examining the effects of different types of conflict irrespective of their secular or religious character. Moreover, event specifications that show the development in fragmentation prior to and after papal (and secular) conflict would have been helpful in judging the validity of the causal identification strategy. Similarly, the book often focuses on the actions of different popes but lumps together the effects of other ecclesiastical actors. For example, Table A.8 finds that monasteries are strongly associated with university foundations. However, given the great variability in the role of education among monastic orders and their generally divergent effects, I would have liked to see a further exploration of the impact of different ecclesiastical groups.

These points, however, are minor and do not detract from the book's remarkable contribution to our understanding of the development of European states. It provides an important corrective to other grand narratives of state formation that fail to pinpoint exactly why modern states emerged first in Europe and not elsewhere. After reading this book, it is hard to see why factors such as war or urbanization that were also prevalent in other parts of the world could have uniquely contributed to European state formation without the presence of the Catholic Church. In this way, the book clearly changes our view of European state-formation, which is no small feat!