The revival of regionalist or substate nationalist movements and/or political parties in Belgium, France, Spain, the United Kingdom and elsewhere in Western Europe during the late 1960s and early 1970s is a story that has been told innumerable times. Although the histories of the affected countries differ, most observers of the phenomenon concur that the reawakening of regionalist political conflict in Western Europe during this period, following its previous quiescence, was the unintended consequence of several common factors: the uneven diffusion of economic and political modernization; the displacement across Western Europe of “traditional” political ideologies, and especially the decline of ideological conflict along the political left–right cleavage; and the “domino effect,” or the imitation by Western Europe’s regional minorities of the strategies for self-determination and self-government adopted by ethnic groups elsewhere in the developed and developing world. Whatever the merits of these and other related explanations, it is indisputable that regionalist conflict and mobilization suddenly surged in Western Europe about a half century ago, and despite fluctuating since, they have persisted under macro-economic and political conditions that, according to numerous scholars, were supposed to precipitate their eclipse.

Against this backdrop and the most recent wave of regionalist political mobilization, a plethora of articles and books on the subject have appeared. Building upon the illuminating scholarship of Margarita Gómez-Reino, Eve Hepburn, Michael Keating, Janet Laible, Peter Lynch, Bonnie Meguid, Lieven de Winter, Ricard Zapata-Barrero, and others, Seth Jolly’s well researched book sheds new light on the political advance of contemporary regionalist movements and political parties in Western Europe. However, unlike most previous scholarship, the primary focus of The European Union and the Rise of Regionalist Parties is not on the internal politics of regionalist parties and movements, the social cleavages from which they spring, and/or their domestic political influence but, instead, on the exogenous factors that facilitate their political success, broadly defined. The book provocatively asks whether the deepening of European integration “encourages regionalist mobilization within European Union member states” (p. 2).

Jolly’s answer, in brief, is that it does. Specifically, he argues that the effects of post-1992 European integration creates “a new political opportunity structure for sub-state regions, such that these small potential states no longer need traditional states to be economically viable” (p. 150). Specifically, the EU’s expansive economic market, public goods, and provision of regional insurance increase the incentive of regions, like Scotland and Catalonia, to aspire to greater political autonomy and even succession (p. 150). Moreover, the enhanced economic and political viability of these aspirant nation-states bolsters the credibility of regionalist politicians and political parties participating in national parliamentary elections (p. 4). In short, instead of undermining minority nationalism, as anticipated by an earlier generation of scholars of the subject, European integration paradoxically has fueled it.

The book systematically advances and supports these arguments throughout five substantive chapters. The first chapter maps out, classifies, and tracks the electoral performance of regionalist political parties in eight countries from the 1950s forward. Chapter 2 posits Jolly’s “Viability Theory,” a causal mechanism that purports to explain how and why European integration facilitates the political success of regionalist parties nationally. According to this theory, European integration diminishes the “advantages of large states vis-à-vis small states, making smaller less heterogeneous states more appealing to regional elites (and citizens)” (p. 41). Jolly’s analysis in Chapter 3 of regional electoral data from the EU 14 countries between 1950 and 2010 allows him to test several variables that potentially explain when regionalist parties choose to compete in national elections and, when they do, the degree to which they succeed. The chapter’s headline findings are that the likelihood a regionalist party will compete in a national election is statistically higher (p. 76) when European integration is deeper and has a “positive and significant effect” on the electoral performance of regionalist parties (p. 84). On the basis of expert survey data and regression analysis of regionalist party positions on the EU, Chapter 4 establishes that, with some notable exceptions (e.g., Italy’s Lega Nord), “regionalist political parties are generally Euro-enthusiastic across issue area, region and time” (p. 92). In the final chapter, Jolly’s analysis of data derived from the 1979 Scottish Election Survey and the 1997 Scottish Referendum Study leads to the conclusion that the 1997 referendum’s success was attributable in part to voters’ diminished unease about the likely consequences of Scottish independence (p. 144).

The rich and varied empirical evidence presented in these chapters clearly substantiates Jolly’s major claims. Specifically, his central argument that the EU’s increasing reach into more policy areas (p. 3) facilitates the political advance of regionalist forces in Western Europe is persuasive. Nevertheless, The European Union and the Rise of Regionalist Parties neglects some key questions. Although it is unreasonable to expect the book to address every question raised by the advance of regionalist parties, it nevertheless does skirt several important ones.

First, given that for somewhat self-evident practical and political reasons the prospect of EU membership for the affected regions is dim, as Jolly all but acknowledges (p. 161), why are a critical number of regionalist voters seduced by this lure? Are they naive, ill-informed, or, alternatively, is there possibly a mediating variable influencing their thinking? Second, as Jolly recognizes (pp. 18–29), many regionalist parties, including the Scottish National Party, are long-lived. Given their deep historical roots, to what degree has European integration facilitated their recent political success? Would the major, pro-EU regionalist parties (e.g., in Spain and the UK) become electorally unviable or simply marginally less successful in the event that EU membership is eventually and widely perceived to be unachievable? Finally, in light of the EU’s comparatively low issue salience for most regionalist parties—a fact that Gómez-Reino and other scholars have underscored and the book ignores—how is it that European integration has had such a positive effect on the electoral performance of these parties? In the specific case of Scotland—the book’s key case study—how does Viability Theory account for the fact that opposition among Scots to a new independence referendum has increased significantly (from approximately 42% to 52%) since the June 2016 Brexit vote?

With these questions unaddressed and unanswered, the analysis presented by the author offers more of a beginning than an endpoint in explaining the political staying power of regionalist movements and parties. Yet this is not a fatal flaw. To the contrary, Jolly should be congratulated for successfully executing, in his words, one of the “first truly comparative, cross-national studies of the incidence and electoral success of regionalist political parties using quantitative analysis” (p. 5). This is undeniably a smart, informative, and well-executed book that advances our understanding of regionalist mobilization in contemporary Western Europe, a major symptom, if not a cause, of national disunity across the region. That said, The European Union and the Rise of Regionalist Parties perhaps raises almost as many central questions as it answers. As a consequence, the puzzle of the staying power of regionalist parties and movements some half century after their resurgence remains substantially opaque.