Chapter 1 offers a historical introduction as well as an overview of existing research in the field. It argues that by mapping out the trajectories of former volunteer soldiers, it is possible to see the many ways in which the Spanish Civil War and the broader anti-fascist engagement of the inter-war period could constitute a transformative experience and event; an event that expanded volunteers’ political horizons and gradually opened up possibilities for border-crossing political engagement in the post-war era. Thus, it sets the stage for the case studies constituting the main part of the book, showing that the political and military influence of the volunteers in Spain did not necessarily come to an end in 1938/1939 or even in 1945. In a few yet significant cases, it stretched across the globe far into the Cold War period.

Chapter 2 examines the history of Leo Kari and other Scandinavian volunteers in the International Brigades. It takes issue with the long-standing depiction of the voluntary army in Spain as ’Comintern mercenaries’ or as essentially the sole invention of international communism. In addition, the chapter follows the trajectories of different members of the resistance movements in Denmark and Norway and examines why historians have typically overlooked the fact that the core of World War II sabotage groups were nearly all former volunteers of the civil war who used their military expertise from Spain to position themselves as leaders of the resistance. Most former war volunteers were completely marginalised in the Cold War climate emerging after 1947–1948, yet some of them still insisted on a third military adventure. The anti-colonial struggles were seen as a new opening, as is evident from Leo Kari’s renewed efforts to mobilise a voluntary army for the Algerian war of liberation in the early 1960s.

Chapter 3 highlights the centrality of Spain in the development of a particular kind of ‘professional revolutionary’ deployed by the Comintern in the late 1930s and 1940s. It focuses on the life of the Italian communist Ilio Barontini and follows his long militancy within the anti-fascist front. Barontini, unlike most Europeans of his generation, had been confronted with violent fascism since the early 1920s. Nevertheless, the Spanish Civil War marks a watershed in his life, as it was in Spain that he refined his skills as a fighter. But Spain influenced Barontini’s trajectory in a political sense, too, as it was during the period of intense fighting at Guadalajara in early 1937 that fellow volunteers in the Italian brigade began to discuss the need to bring the anti-fascist fight to the colonial front as well. In the following years, Barontini went both to fight and to train new recruits in Ethiopia, France, and Italy. In this way, the chapter offers a glimpse of one way in which anti-fascism and anti-imperialism connected in this period.

Chapter 7 elaborates on the extensive empirical corpus analysed in the preceding chapters. It reinforces the comparative points and clarifies the general patterns emerging in the book. It also expands our reflections on the meanings of modern transnational war volunteering, especially as seen through the conceptual lens of internationalism. The chapter presents conclusions regarding the ideological and organisational dynamics of transnational war volunteering as a left-wing political practice in the twentieth century. These findings open up new perspectives on mobilisation patterns pertaining to transnational volunteering, potentially moving the discussion away from top-down directives or impersonal indoctrination tools to a greater appreciation of the significance of contingency and horizontal influences shaping volunteer behaviour. Elaborating on these findings, the concluding chapter thus offers new conceptual registers to comprehend the phenomenon of left-wing war volunteering in the twentieth century.

Chapter 5 follows a small but diverse group of Cuban Spanish Civil War volunteers, paying particular attention to Rolando Masferrer and Eufemio Fernández. The post-Spain trajectories of these volunteers illustrate the volatile nature of politics in Cuba and the Circum-Caribbean in the 1940s and 1950s, where coalitions were consistently made and unmade in transnational efforts to topple regional dictators. Later, several Spanish Civil War volunteers came to occupy influential roles as strategists and instructors within the military structures that the Castro regime developed to support revolutionary movements in the Americas after 1959. Thus, Cuban politics offered an unusually large and varied number of opportunities for Spanish Civil War veterans to remobilise after their service in Spain and to continue to engage with armed revolutionary projects of a transnational or internationalist nature.

Chapter 6 offers an analysis of the Nicaraguan Revolution with a particular focus on Araceli Pérez Darias, a Mexican citizen of Spanish descent fighting with the Sandinistas on the Western Front in Nicaragua during the late 1970s. She was ambushed, raped and killed in 1979. Using Araceli’s life story as a prism, this chapter offers a unique survey of women’s contribution to transnational warfare in the twentieth century, arguing that their challenges were multiple. Unlike their male comrades in arms, they were generally not allowed to fight at the front. Further, they were often subjected to abuses, and their armed resistance – originally motivated by their opposition to the enemy – eventually became intertwined with their struggle to be accepted as equals by the movement they represented at the front. In addition, the chapter provides the first comprehensive overview of the foreign brigades fighting for the Sandinistas, explaining why some have survived in the collective memory of the revolution while the most decisive of them all, consisting of Panamanian volunteers, were cast into oblivion.

Chapter 4 follows the trajectory of Ernst Frey and other European anti-fascists, who enlisted in the Vietnamese Army after defecting from the French Foreign Legion. It focuses on the complicated relationship between the soldiers who survived the anti-fascist struggles in Europe and the new generation of soldiers of the anti-colonial wars in the Global South. After 1945, many Spanish Civil War veterans followed events in Algeria and Indochina with great interest and sided with those fighting for national self-determination. Notwithstanding the visibility of both causes, notable armed support materialised only in Indochina, where foreign volunteers were initially well-received and saw their military influence grow much beyond what their modest careers in the French Foreign Legion might indicate. With time, however, they were also seen as a challenge to the nationalistic Vietnamese leadership, who, thanks largely to Chinese support from the early 1950s onwards, were radically altering their military structure, leaving little or no space for French Foreign Legion defectors.