Philip H. Stump’s latest book is a major contribution to conciliar movement studies, offering a new approach to the Council of Constance’s successful efforts in bringing the Great Western Schism to an end. Building on his earlier work on the Council’s reforms (The Reforms of the Council of Constance (1414–1418), Leiden: Brill, 1994), the author examines how conciliar diplomacy and political pragmatism helped to end the nearly four-decade-long division in the Latin Church. Engaging critically with primary sources and existing historiography, the book situates the Council not merely as a theological or juridical assembly but as a diplomatic actor operating within the highly complex political context of the early fifteenth century.

The Preface opens with a comprehensive reflection on historiography, discussing diverse approaches to conciliar studies. This valuable dialogue with both recent and established scholarship continues throughout Stump’s study. Drawing on a recent interpretive framework that views the Schism through an anthropological lens of conflict and conflict resolution (Joëlle Rollo-Koster, The Great Western Schism, 1378–1417: Performing Legitimacy, Performing Unity, Cambridge: Cambridge University Press, 2022, and her earlier works), the author adopts a cultural approach that foregrounds conciliar diplomacy as an example of the Council’s performance of legitimacy and unity, characterized by a process of consensual decision-making. Cautiously navigating the divergent views of conciliar scholars such as Paul Avis, Francis Oakley, Walter Brandmüller, and Ansgar Franken, the book benefits from the historiographical renewal sparked by the 600th anniversary of the Council of Constance, placing its history within a broader global context. Accordingly, the Introduction establishes nine analytical frameworks that set the tone for a study that integrates ecclesiastical, political, and diplomatic history.

Structured into eight chapters, the main body of the book follows a broadly chronological order and traces the Council’s trajectory from the aftermath of the Council of Pisa to the papal election in 1417. The first two chapters establish both continuity and rupture with the earlier assembly, highlighting the shift from papal to conciliar control over the Council of Constance, particularly following John XXIII’s flight. Through a detailed exploration of the Council’s nation-based consensus model and its dealings with rival popes, Stump convincingly illustrates the mechanisms by which conciliar legitimacy and authority were constructed. Chapters 3–5 explore the Council’s engagement with rival obedience, culminating in the depositions and abdications of all three popes. A notable contribution here is Stump’s detailed account of the conciliar diplomatic efforts with the Iberian kingdoms, carried out in close synergy with Sigismund of Luxembourg, whose political skills Stump holds in high esteem. These chapters, grounded in extensive analysis of historical sources, particularly the Capitula Narbonesia, highlight the Council’s pragmatic and regionally adaptive strategies. In the following chapters, the narrative broadens to include two further subjects: the roles played by women, such as Empress Barbara of Cilli and Queen Joanna II of Naples, “in the synergistic conciliar diplomacy” (154), and the intricate financial networks that sustained the Council and its activities. Partially based on Stump’s earlier studies on fiscal reform, these sections enrich the analysis with perspectives often absent from earlier institutional histories of the Council of Constance. The final, eighth chapter, titled “dénouement,” reflects on the conclusion of the Council’s dual mission: ending the Schism and initiating reform. Although Martin V’s election marked a formal return to church unity, Stump remains attentive to the “priority struggles” between the two main conciliar tasks and to the ambiguities surrounding the final outcome. Nonetheless, the analysis stops short in November 1417, leaving the legacy of conciliar diplomacy somewhat overlooked. In the Epilogue and Conclusion, Stump offers a broad overview of the fifteenth-century political history and proposes several general remarks on the role of consensus and synergistic diplomacy in achieving peace. The book ends with three appendices, including guidelines for consulting the conciliar acts (1) and short descriptions of lesser-known primary sources (2 and 3).

In sum, Stump’s book is richly researched, skilfully written, and interpretatively ambitious. The author demonstrates impressive mastery of multilingual primary sources as well as both recent and established historiography. The combined diachronic and synchronic approach allows him to situate the Council of Constance within broader historical frameworks, weaving together diverse strands of analysis into a compelling and accessible narrative. However, the narrative pacing is uneven. While the central chapters offer dense, rewarding analysis, the final reflections on Martin V’s election and the Council’s post-1417 situation feel abrupt, especially given Stump’s prior contributions to revising views on Martin’s approach to reform. One might also wish for a critical discussion of the Council’s engagement in broader European political rivalries. The Council’s role as a “peacemaker in secular conflicts” (23), as Stump briefly acknowledges, has not yet been fully explored. Given that political conflicts were often understood in spiritual terms, as both causes and consequences of ecclesiastical division, the resolution of the doctrinal and ecclesiological crisis caused by the Schism was, for the Council’s members, intrinsically linked to the resolution of political strife. Moreover, the Polish appeal for a new council in 1418, which occurred after the election of Martin V, underscores the enduring expectations placed upon the Council as a mediating instance. Finally, some minor editorial oversights should also be noted, for example, 1498 instead of 1398 (63, fn. 20) or a missing letter in “priority strugges” (188), which do not detract from the book’s academic value. Nevertheless, students and scholars alike will find in Stump’s study a comprehensive guide and an essential reference for future research on the Council of Constance and ecclesiastical diplomacy in the late Middle Ages. The book’s relevance extends even beyond medieval studies: at the beginning of Leo XIV’s pontificate, when questions of synodality and institutional authority are once again at the forefront of ecclesiological debate, Stump’s analysis offers an instructive insight into broader themes of political representation and conflict resolution.