Fortification of interstate borders has been on the rise, with dozens of countries erecting barriers to movement in an effort to stem cross-border migration and smuggling. Recent cross-national studies suggest that most of these barriers are designed to limit migration from poorer countries to their wealthier neighbors (David B. Carter and Paul Poast, “Why Do States Build Walls? Political Economy, Security, and Border Stability,” Journal of Conflict Resolution, 61 [2], 2017; Ron E. Hassner and Jason Wittenberg, “Barriers to Entry: Who Builds Fortified Boundaries and Why?” International Security 40 [1], 2015). In this book, Nazli Avdan challenges this finding, presenting evidence that certain types of terrorism (targeting of the country's territory and citizens) lead to tightening of border controls (primarily visa restrictions), thereby arguing that security concerns shape border controls. Despite the focus on security, her analysis also shows how economic interdependence in some cases attenuates and even trumps security concerns. Overall, this book demonstrates that responding to terrorist threats requires walking a fine line. On the one hand, security concerns increase the demand for border protection, but on the other hand, tighter border controls can lead to adverse economic consequences.

Chapter 1 lays out the theoretical basis for the investigation and discusses the main concepts that it uses in the rest of the analysis. Avdan draws a distinction between global threats that do not involve a state's territory or citizens and targeted threats that involve either the state's territory or its citizens. This distinction is the key to her empirical analysis and also yields some of the more original and interesting findings that her book brings to the literature on border controls. Her theoretical argument produces three predictions: (1) terrorism heightens security concerns and leads to a higher demand for border protection; (2) threats against a state's territory or citizens have a stronger impact on demands for security and border control than global threats; and (3) trade and capital ties between states attenuate the effect of security concerns on border control.

In chapter 2, Avdan explores how terrorism and economic ties affect visa restrictions in a dyad (pair) of countries. She analyzes data from 189 states and 18 political entities. Her main findings suggest that visa restrictions are positively associated with both global and targeted terrorism but are negatively related to bilateral trade. She also presents marginal effects of an increase in terror attacks on visa restrictions for different levels of bilateral economic ties. The overall discussion is very transparent and easy to follow, but some of the findings are puzzling. For example, Figure 1 seems to suggest that, above a certain level of bilateral trade, global terrorist attacks by citizens of the origin country make visa restrictions against citizens of that country less likely compared to visa restrictions against countries with a similar level of trade but whose citizens did not conduct attacks. This is a very strong and precisely estimated result, but the theory does not explain it.

Chapter 3 focuses on visa rejection by the European Union (EU) countries. The analysis introduces some new control variables that were not used in the previous chapter, such as an indicator of whether the origin country is majority Muslim. Overall, this analysis supports the argument that whereas security threats have a positive relationship with the visa rejection rate, economic ties have a negative effect. Some of these findings raise additional questions. For example, Figure 5b suggests that higher levels of dyadic foreign direct investments (FDIs) are associated with higher visa rejection rates following an increase in targeted terror attacks. This finding is at odds with the general argument and the findings with respect to trade salience, and it is left unexplained.

In chapter 4, Avdan examines the determinants of border walls. Using a simple frequency table, she demonstrates that whereas global attacks are very weakly related to border fortification, targeted attacks against a country's territory and citizens exhibit strong positive association with border walls. This is indeed one of the novel findings of her book. Regression analysis, however, only partially supports this finding. Results suggest that, although targeted and fatal attacks may appear to be positively correlated with border wall construction, this association is due to some dyad-level underlying factors (fixed effects). Interestingly, high-impact (spectacular) attacks are not associated with a particularly high likelihood of border fortification. The results also suggest that trade relations between countries are not a good predictor of border fortification. Instead, wealthy countries are more likely to erect border fences, especially against populous neighbors, which is similar to findings in previous studies.

Chapter 5 focuses on the Turkish case. Avdan explores how economic liberalization and change in the conflict environment affected Turkey's visa and border control policies. Her analysis here suggests that Turkey retained liberal visa policies with respect to Western European countries—largely for economic reasons and because it wanted to join the EU—and did not retaliate despite occasional restrictions on Turkish nationals in those countries. In contrast, Turkey’s policies toward the Middle East were more affected by security concerns, especially following ISIS attacks in major Turkish cities. Although the general trends in the Turkish case are consistent with the hypotheses of this book, Avdan could have considered more thoroughly alternative explanations, such as the influx of Syrian refugees that has somewhat coincided with changes in border control policies (Anna Getmansky, Tolga Sinmazdemir, and Thomas Zeitzoff, “The Allure of Distant War Drums: Refugees, Geography, and Foreign Policy Preferences in Turkey,” Political Geography 74, 2019).

In the concluding chapter, Avdan highlights the relevance of her findings for broader themes such as globalization, migration, populism, territoriality, and crime. Overall, she makes several important contributions. First, she highlights that border control is a multifaceted policy area. Most of the scholarship so far has focused on visible policies, such as border walls. By analyzing visas and connecting them with the threat of terrorism, Avdan suggests that some of the border controls can be implemented in subtler, less visible, and more nuanced ways. More importantly, although terrorism may not have a robust impact on the establishment of border walls, she shows that it affects migration and mobility through visa requirements and rejections. One of the key implications of her analysis is that terrorism can have indirect negative effects on the compatriots of the perpetrators, who face a higher likelihood of access denial from countries targeted by these attacks. Another innovative finding relates to visa denials to citizens of majority-Muslim countries. Although most of the recent attention has focused on President Trump’s travel ban against citizens of several Muslim countries, Avdan convincingly shows that similar policies are also prevalent in the EU: applicants from Muslim countries are significantly more likely to be denied a visa, controlling for many factors that may affect visa policies.

This book also paves many avenues for future research. One is further exploration of the connection between economics and security. Avdan assumes that there is a trade-off between security measures and economic cooperation. However, in reality, conflict also imposes economic costs. Thus, a more complete analysis of how economics shapes border controls should incorporate the economic costs of addressing and not addressing security concerns.