Why do some movement-based parties develop top-down organizational structures, whereas others maintain organic linkages to their grassroots bases? Stated differently, how can political parties escape the iron law of oligarchy? This theoretical and empirical puzzle is at the heart of When Movements Become Parties: The Bolivian MAS in Comparative Perspective by Santiago Anria. The conventional wisdom, based on the seminal work of Robert Michels in Political Parties (1911), suggests that all parties, regardless of their origins, eventually and inevitably develop oligarchic or elitist tendencies that are associated with increased bureaucratization and specialization. Anria proposes that this may not always be the case.

Based on a carefully crafted comparative within-case research design focused on Bolivia’s governing Movement toward Socialism (MAS) party, Anria argues that the organizational strength, density, and autonomous capacity for social mobilization by popular constituencies form the causal mechanism that prevents a party from falling victim to oligarchic temptations. He provides a structuralist explanation for MAS’s political behavior, demonstrating that its genesis—its origins and early institutional development—in the highly organized and disciplined social movement of the coca growers, in conjunction with civil society’s ongoing capacity for autonomous mobilization to shape internal power distributions, leadership patterns, and the party’s organizational model, is the secret to its avoidance of top-down organizational attributes. His well-researched and well-analyzed book sheds new light on the internal politics of the MAS in a field dominated by studies of the emergence and spectacular rise of this highly successful movement-based party.

Studying the MAS is akin to examining a prism: what you see depends on your vantage point. Up close, from the perspective of social movement organizations, the MAS may appear to behave as a conventional, co-optative political party or as a participatory, grassroots-led political movement. According to Anria’s findings, the view from the cities of the western highland plateau and the eastern lowlands is that of a party that relies on top-down mobilization strategies and co-optative practices that, at times, threaten the autonomy of allied social groups. In contrast, the view of the rural coca growers from the highland valley region, the birthplace of the MAS, is that of a bottom-up organization with organic movement–party linkages through which the bases wield significant control over its development (p. 68). The ability of the MAS to look and operate differently in rural and urban sectors, which Anria characterizes as part of its hybrid nature (see Chapter 2), is determined by the structural configuration of civil society and its propensity to align with the party.

From the perspective of democratic theorists, the MAS may seem unacceptably illiberal or impressively inclusive. Whereas liberal theorists lament the erosion of civil and political rights and freedoms under President Evo Morales, even to the point of characterizing contemporary Bolivia as nondemocratic, direct or participatory democratic theorists, such as Anria, applaud the significant advances under the MAS in increasing the inclusion and participation of society’s most marginalized sectors (p. 225). It is clear from this discussion that interpretations of the impact of the MAS both at the societal and political levels are highly polarized. Anria is refreshingly unapologetic in his assessment of MAS’s internal politics and supports his assertions with compelling fieldwork observations and interview data, as well as public opinion and electoral data.

The book is divided into five chapters. The national and municipal electoral data maps that accompany the text help illustrate the dramatic political and territorial expansion of the MAS in less than a decade. The introduction outlines the basic contours of the central argument and assumptions of the book. It highlights the benefits of bringing “society back in” to party analysis by stressing that social movements may not only become parties but are also a critical factor in explaining parties’ organizational structures and operations (p. 26). Chapter 1 establishes the theoretical framework of the book and its methodology. Particular attention is paid to the Michelsian challenge. Anria argues that the MAS has been able, at least to a certain extent, to overcome its oligarchic tendencies because of what he terms “historical causes” that are traceable to the party’s origins and “constant causes” linked to its power bases, which together provide countervailing pressures that limit hierarchy and concentrated authority.

In Chapter 2, Anria traces the origins and ascendance to power of the MAS. He claims that the MAS is a hybrid party that is built on two distinctive coalitions: (1) a core coalition or constituency based in the countryside that consists of the coca growers of the Chapare region, as well as the country’s three national-level peasant confederations, and (2) a peripheral coalition consisting of a more heterogeneous set of urban and popular sector organizations. Chapters 3 and 4 represent the empirical heart of the study. Chapter 3 provides a fine-grained analysis of candidate selection processes within the MAS and the geographical unevenness of grassroots input into party nominations. Chapter 4 analyzes the role of civil society actors in the national policy decisions of the MAS. Anria finds that grassroots influence varies significantly by policy area depending on the relative power or “constraining” and “creative” capacities of organized social bases. Chapter 5 tests the generalizability of the book’s argument by comparing the organizational development of the MAS with two other movement-based parties in the region: the Workers’ Party (PT) of Brazil and the Broad Front (FA) of Uruguay. The book concludes with a nod to the broader significance of the author’s findings and new avenues of inquiry into party–social movement dynamics.

When Movements Become Parties is provocative in its assertion that the Bolivian MAS may be the exception, at least partially, to the iron law of oligarchy. According to Anria, the goal of the book is not to refute this iron law, but rather to uncover the conditions, mechanisms, and processes under which grassroots participation can be promoted and sustained within political parties (p. 6). This is an important academic task. The findings of the book, however, point to an exceptional constellation of factors in the Bolivian case, including the presence of a weak state and a strong civil society, which may not be replicable or even desirable elsewhere. The assumption that autonomous social mobilization by popular constituencies is an effective check on executive power in Bolivia (p. 94) is contentious.

Clearly, Anria’s work makes a substantial theoretical and empirical contribution to the literature on movement-based parties and on the potential trade-offs between representation and participation of the masses in Latin America. There is much to commend in this book, just as there is much to provoke discussion and debate among political scientists. As Anria admits, the book is about the story of the MAS as of 2018 (p. 11). The 2019 presidential elections, which carry the distinct possibility of a fourth presidential term for Morales, may bring about the most undemocratic period in the MAS’s history. But that potentially unhappy story is a tale for another day.