At a time when state borders in Eastern Europe are again challenged militarily, a book about the military frontier between the Habsburg and the Ottoman Empires (1553–1881) feels almost discomfortingly timely. However, Bogdan G. Popescu does not study the military frontier as an institution of defense. He uses this case to advance our understanding of the relationship between state authority and peripheral social institutions, combining James Mahoney’s insight that the effect of colonialism on contemporary development depends on pre-colonial institutions (Colonialism and Postcolonial Development: Spanish America in Comparative Perspective, 2010) with Robert Putnam’s theory of social capital (Making Democracy Work: Civic Traditions in Modern Italy, 1993). Historians have already highlighted the contribution that this truly interdisciplinary book makes to Habsburg historiography. This review complements them by focusing on its contribution to comparative politics.

Using a multi-method design based on the meticulous collection and analysis of primary and secondary, qualitative and quantitative, historical and contemporary data, “Imperial Borderlands” traces the material (under-provision of public goods) and ideational legacies (civic disengagement and low social trust) of the monarchy’s decision to strengthen patriarchal clans of settler families in its military border region. My main and only criticism of this exceptionally rigorous piece of social research is that Popescu decided to frame his book prominently around a theory of varieties of extractivism that can only partially be assessed with the chosen research design. This framing may lead readers to underappreciate another important theoretical insight, one that does follow from the empirical analysis: that states can benefit from reinforcing (rather than undermining) pre-existing family structures in their peripheries, and that this has lasting effects on social capital.

Popescu classifies the Habsburg military frontier as an instance of extractive colonialism, defined as the “transfer of economically valuable resources from indigenous groups to the imperial center” (p. 33). Instead of raw material, military colonialism extracts military service from border populations—a cheap alternative to conventional soldiers. The theoretical chapter (Chapter 2) builds a typology of extractivist institutions that classifies them along three attributes: (1) high versus low investment in local infrastructure; (2) removal versus non-removal of property rights; and (3) use of violence. The typology explains why extraction is sometimes associated with worse, and other times with better developmental outcomes. As Popescu argues, outcomes will be worse if the resources to be extracted require low investment in infrastructure, and if extraction goes hand in hand with acts of violence and the removal of individual property rights. The Habsburg military frontier is an instance of such a worst-case scenario (though not an entirely clear-cut one, since, as in the other cases of military colonialism discussed in Chapter 7, property rights were not in fact removed, but granted collectively to border communities).

Based on this setup, one might have expected the main empirical chapters (Chapters 3–6) to test which of the extractivist regimes leads to better, and which to worse developmental outcomes. Instead, these chapters study the Habsburg military frontier in-depth, comparing the border area (where military service was “extracted”) to the immediately neighboring civilian area—all in what is nowadays the Republic of Croatia. This is a sound design to assess whether Habsburg-style military colonialism left a lasting mark on the former periphery. It is less adequate for capturing whether one type of extractive institutional regime leads to worse developmental outcomes than another. Covering all theoretically possible constellations (three attributes times two possible values) would require comparing six extractive regimes. Chapter 7 indeed heads in that direction; it gives an insightful overview of Russian and French versions of military colonialism. These cases vary on infrastructure (better developed than in the Habsburg case) and violence (less intense), but the chapter does not test whether this leads to different developmental outcomes. (The third feature, communal property rights, is present in all three cases because the Russians and the French copied this strategy of incentivizing border dwellers to become border protectors from the Habsburgs).

The theory of extractivist regimes is insightful in its own right, and future research can take Chapter 2 as a basis for comparative studies. However, I strongly recommend readers pay close attention to the book’s second theoretical contribution, laid out across its empirical Chapters 5 and 6. These offer a rigorous investigation of the long-term consequences of the state’s decision to reinforce, rather than undermine a pre-existing social institution characteristic of its periphery, the zadruga.

A zadruga is a clan consisting of two or more families. Due to its patriarchal, hierarchical set-up, Popescu characterizes it very poignantly as “a micro-Leviathan within the borderlands of the Habsburg Empire” (p. 169). In return for trans-generationally committing younger males to military duty, zadrugas within (but not outside) the border region received plots of land from the monarchy and were exempted from serfdom. As a social institution, zadrugas were also common in the civilian area. Yet, it was only in the military area that the monarchy (1) eliminated feudal lords as an alternative source of social power competing with clans’ elders, (2) assigned land titles to the clan as a collective and (3) prohibited individuals from exiting it. In this way, the Habsburgs reinforced the social norms typical of zadrugas: hierarchical governance, patriarchy, positive bias towards clan members, and distrust of non-members.

The careful analysis of historical sources and ethnographic studies in Chapter 5 (in combination with parts of Chapter 3) sheds light on the inner workings of zadrugas and on the state’s rationale for working with clan elders to exercise control over locals. Chapter 6 then estimates the causal effect of the border region on a variety of attitudes and values using a regression discontinuity design that compares the area that was inside the military frontier to immediately neighboring areas. The rigorous multi-method design convincingly demonstrates that where the “micro-Leviathans” were strengthened by the “macro-Leviathan,” they left a lasting imprint. Border populations continue to score lower on several contemporary measures of social capital and civic engagement.

This second contribution replaces a simplistic view of peripheries as either ungoverned or assimilated with a theoretically much more compelling conditional argument that combines Mahoney’s and Putnam’s reasoning. Where Mahoney compared places where pre-colonial political institutions were in place to those where colonizers built institutions from scratch, Popescu shows that the more subtle difference between areas where colonial centers strengthened traditional social institutions and areas where they did not can also leave long-lasting effects. And where Putnam saw the social capital that develops in what he calls “civic communities” as exogenously determining the performance of state institutions, Popescu shows how state institutions can themselves integrate and strengthen older social institutions. It is with these findings that “Imperial Borderlands” is sure to leave a lasting impact of its own, namely on our understanding of how states govern their peripheries through the integration of family structures.