This book aims at understanding competition between armed groups in civil wars. Using the market labor literature, Mironova unravels why certain groups became powerful at the expense of others and the rationale of the fighters in choosing certain groups. Mironova conducted more than 600 interviews, surveys and focus groups, mainly with former fighters, and she was embedded with the Kurdish Army and the Iraqi Special Operations forces. Based on rich first-hand knowledge, Mironova analyses several armed groups, such as al-Nusra and ISIS, ranging from powerful ones with a large member base to groups that only survived a few months. The findings are quite convincing. Mironova explains that armed groups operate as an industrial firm, offering the best benefits and supplies to attract the best fighters. In fact, ‘a group that aspires to dominate must be appealing to potential group members’ (p. 45). Fighting on the same side and switching groups was quite common, and all the groups were interested in attracting the best fighters. Competition affected both local and foreign fighters, although foreigners were sometimes more interested in non-material benefits. Moreover, rebel group competition is useful for understanding post-war processes. If the opposition wins, the most likely to take power are the most powerful rebel groups, the better organised and funded. The book is an incredibly useful resource for understanding the rational decision-making processes of actors in a civil war. Although Mironova analysed mostly rebel groups in the Syrian and Iraqi civil war, her aim is to build a general theory on armed groups' human resources. In this light, further steps are to verify the theory in other multifaction civil wars.