In States in Disguise, San-Akca examines the determinants of cooperation between states and rebel groups in the period after the Second World War. The book is closely related to previous work in political science that has highlighted the transnational dimensions of civil wars and identified the determinants of external state support for rebel groups fighting civil wars against other states. San-Akca's book builds on this body of work and advances our understanding of the relations between states and rebel groups on conceptual, theoretical, and empirical grounds with great success.

On the conceptual side, San-Akca distinguishes between states’ intentional and de facto support for rebel groups. Intentional support covers cases in which states deliberately support rebels as a method of pursuing their own foreign policy objectives, whereas de facto support covers cases in which rebels select a state unilaterally for operations and resource acquisition without necessarily securing the knowledge and approval of that state. The former category is well known to scholars of conflict, especially in the form of proxy wars. However, San-Akca convincingly demonstrates that in several examples of armed conflict, rebel groups have behaved autonomously and operated in states without their approval. To give a current example, the ISIS presence in Europe is a case of de facto support by European countries, according to San-Akca's conceptual distinction.

Having made this distinction, States in Disguise provides a novel theoretical framework that focuses on the triadic interaction between the rebel group, its supporter state, and the target state. Within this interaction, three types of factors determine both the onset and the level of intentional and de facto state support for rebel groups: a) states’ material interests, b) ideational affinity between target and supporter states as well as between supporter states and rebel groups, and c) supporters’ domestic incentives. More specifically, San-Akca's key hypotheses are that states are more likely to support rebel groups that target an adversary state if there are ideational ties between the state and the rebel group, and if the supporter state faces domestic unrest and therefore has difficulty in mobilizing its domestic resources and populace. Rebel groups also seek support from their targets’ adversaries, with whom they share ideational ties. Whether rebel groups seek support from strong or weak states depends on how much they fear possible retaliation by the target and how much they care about preserving their autonomy. Rebels are also more likely to choose democratic states because they allow groups to organize more easily relative to autocracies.

San-Akca tests these hypotheses by using a new non-state armed groups dataset, which in itself is a significant contribution to the study of armed conflict and its international determinants. She has identified 455 non-state armed groups that were active around the world in the period between 1945 and 2010, along with their targets and supporters. The dataset also includes information on the types of support these groups received, such as safe havens for group leaders and members, training camps, provision of training, headquarters, weapons, logistical support, financial aid, and transport of arms, military equipment, and supplies. Cases of intentional support also include troop support. To capture the importance of ideational ties between states and rebel groups, San-Akca also has coded the ethnic, religious, and ideological characteristics of rebel groups.

The empirical analysis presented in States in Disguise provides strong support for San-Akca's theoretical expectations. She finds that states are most likely to provide intentional support to groups that target their adversaries and when they are also troubled domestically and do not have conventional state allies to call for help. San-Akca's explanation for this finding is that states delegate their external wars to rebel groups during times of heightened domestic instability. States are also more likely to support groups that are ethnically, religiously, or ideologically similar, and by extension, less likely to support rebel groups that target states with an ethnic, religious, or ideological identity similar to their own. Rebels on the other hand look for support from strong and democratic states. Ideational ties between supporter-state and rebels also matter. Rebels are especially more likely to seek de facto support from a state if the rebels share the same ethnic identity with one of the minority groups in the supporter state.

The book also includes two brief case studies of intentional and de facto support. The first is a study of the various Palestinian groups who have fought Israel, and the motivations of the states that support them. The second is a study of the groups that fought against Chad, and their motivations in choosing different states for de facto support. Both studies highlight the patterns of state-rebel group cooperation that San-Akca's theory focuses on and enrich the book's empirical sections, which are based on statistical analyses. However, similar to the discussion of Egypt's lack of support for Palestinian militant groups, the case study of groups fighting in Chad could perhaps more extensively examine why some rebel groups received significant backing while others did not.

Overall, San-Akca's book is a significant contribution to the study of state-rebel group relations for two reasons. First, it highlights empirically the importance of ethnic, religious, and ideological ties in determining state support for rebels, going beyond states’ material interests. Second, the book provides a new dataset with detailed information on the types of support enjoyed by autonomous rebel groups across the world. The findings reported in the book and the dataset promise to be essential resources for future researchers of the relationship between domestic conflict and international factors.