In 1989, for the first time in six decades, the state of Baja California elected a governor who did not belong to the Partido Revolucionario Institucional (Institutional Revolutionary Party, PRI), thereby paving the way for the democratisation of Mexico. This was also the beginning of the most violent period of recent Mexican history. Votes, Drugs, and Violence tries to understand how Mexican democratisation and criminal violence are related by addressing three questions: Why did Mexican cartels go to war as the country transitioned to democracy? Why did violence increase as fundamental democratic features took root in the federal system of Mexico? And finally, why did drug cartels launch important attacks against local political actors and develop an interest in becoming local de facto rulers?

At the outset of the book, the authors elaborate on the notion of the ‘grey zone of criminality’, an area in which state agents provide the protection that organised criminal groups (OCGs) need to exist. The book claims that authoritarian regimes, along the lines of Mexico from 1929 to 1989, are characterised by these grey zones, tolerating criminal behaviour in their allies, while at the same time encouraging unlawful repression of their opposition. Drawing from historical sources, the authors demonstrate that the first Mexican drug cartels were protected by the authoritarian PRI government. Following a partial liberalisation of the regime in the 1970s and 80s, state power was transferred from the federal government to Mexico's 31 states. Guillermo Trejo and Sandra Ley argue that as these subnational units started to be governed by opposition parties, drug cartels lost state protection and took the unprecedented decision to form private militias, to compensate for the loss. Remarkably, some of the recruits were defectors from state security forces who did not face trial and remained active in public life. Although these militias were used initially for defence, they quickly became an instrument with which to dispute the territory of unprotected rival drug cartels, and to co-opt or attack state officials who refused to collude with them.

A key contribution of the book is presented in Chapter 4, which analyses how the War on Drugs launched by President Calderón in 2006 influenced criminal violence. Many scholars have studied different elements of this federal intervention, from the effects of the ‘kingpin strategy’ to the logistic difficulties of coordinating a coherent strategy by a fragmented state. However, no one before had paid close attention to its politicisation (that is, its use for partisan electoral purposes): a crucial aspect to consider in the polarised political context of 2006 Mexico. Trejo and Ley show that the lack of reforms to the security forces and the judicial system enabled post-authoritarian elites to maintain tight control over these two bodies. This allowed President Calderón to derive electoral benefits from politically biased federal interventions. Thus, in states controlled by his Partido Acción Nacional (National Action Party, PAN), the federal government cooperated across different levels of government to control violence and obtain electoral benefits. On the contrary, in states governed by the opposition Partido de la Revolución Democrática (Party of the Democratic Revolution, PRD), the federal authorities refused to cooperate with different levels of government and blamed the opposition for the increase in violence. To prove that it was not a matter of coordination between different parties, as some scholars have argued, Chapter 5 demonstrates with in-depth case studies how the federal government did manage to cooperate in states governed by the PRI.

Part 4 of the book explores the transformation of drug cartels into de facto local rulers after prolonged criminal wars, and debunks the assumption that OCGs do not have political goals. Thus, it deconstructs the distinction held in the armed-conflict literature between criminal and political violence. The authors show that, in the quest for resources to finance criminal wars, drug cartels learnt that controlling municipal governments implied access to valuable resources and protection. As a result, drug cartels began to launch attacks on local political actors in states that were unprotected by the federal government due to partisan conflicts, and during election cycles when there were more opportunities to influence the composition of the next municipal administration. By relying on statistical analyses, natural experiments and in-depth interviews, the authors show that drug cartels developed political interests, proactively influenced subnational politics and became de facto local rulers. The consequence of this is a deepening human-rights crisis as civil society is unprotected (or even attacked) by a subverted state. To break the state−crime nexus and avoid the emergence of democratic dynamics connected to the criminal underworld, Trejo and Ley suggest the implementation of profound reforms to the security and judicial sector or transitional justice processes.

If Votes, Drugs, and Violence does a great job in showing theoretically and practically how authoritarian regimes contribute to the formation and consolidation of the grey zone of criminality, it tells us little about how these zones can (or cannot) reproduce themselves in liberal democracies. Although it is mentioned that these grey zones are narrower in liberal democracies, we are not told how it is possible that most illegal drugs are consumed here. If liberal democracies enjoy relative peace and prosperity, it is probably through the export of violence to developing countries − a dynamic exemplified in the flow of guns from the United States to Mexico − something the book is unable to look at due to its subnational focus. Similarly, there is no discussion on the pertinence of drug regulation for the reduction of violence, a remarkable absence given that such an approach has been increasingly suggested by scholars, activists and policy-makers as one solution to the problems.

Such gaps, however, do not diminish the impact of the book for the development of a ‘political science of organized crime and large-scale criminal violence’ (pp. 8, 27, 291–2) and it has valuable lessons for students of the state, organised crime, armed conflicts, and democratic transitions. Better understanding of these grey zones is a particularly pressing issue for the increasing number of people around the world who now live under criminal governance regimes supported by state officials.