This is one of those questions where it really matters which set of foreign volunteers we’re talking about. Their post-Spain trajectories vary immensely, with the most important single factor being their nationality. Given the rapid changes in European geopolitics in 1936-9, it’s not hard to imagine how this might have affected a significant number – the Austrians, for instance, saw their home country disappear entirely while they were in Spain. For others, notably the considerable number of Germans and Italian volunteers, it’s also easy to see why they might not be eager to return home and put themselves at the mercy of their governments, so they ended up in limbo until they were swept up in the Second World War in various ways. Other contingents, such as the French, British and Americans, had a relatively easier time of things but still had difficulties of various sorts. There are also quite a few outliers – there were some prisoners of war held by the Nationalists, some of whom remained prisoners into the 1940s, and others were in Republican jails, imprisoned for civil or military crimes against the Republic, some of whom were only released when the Republic started to collapse and their guards left their posts.

Even for the majority of foreign volunteers, the drawn-out process of their withdrawal led to distinct outcomes. The decision was taken to withdraw the volunteers in late September 1938, the Republican Government agreeing to do so in the vain hope of putting political pressure on the Italian Government to withdraw direct support from Franco (not to mention that the International Brigades, now completely starved of foreign reinforcements, were no longer especially effective). The c.10,000 remaining foreigners were withdrawn from the front shortly after, and there was a large, emotional farewell parade in Barcelona in mid-October. But the diplomatic complexities of the process caused delays. For the British, for instance, arguing about who was going to pay for their transport home took a couple of months to sort out – for the homesick volunteers, this was a frustrating period, and was eventually only solved when each volunteer agreed to repay their repatriation costs to the British Foreign Office (most never actually did). Such difficulties meant that volunteers only left Spain slowly over the rest of 1938. Many were wounded or sick, adding further complications to their repatriation. Generally, however, citizens of powerful countries (especially those who were willing to use diplomatic pressure to secure the safety of their citizens as a matter of principle) made it back to their homelands eventually.

Those who returned soon went their different directions – many continued trying to campaign for the Spanish Republic (and, later, for their old comrades in various sticky situations) politically, others avoided politics altogether, a minority had become embittered and denounced the International Brigades themselves. A significant number ended up fighting again as part of their home countries’ militaries during the Second World War, but there are many complications, such as Communist Party (to which many belonged) hostility to the war up to June 1941, and the extent that they were distrusted by their home governments due to their actions in Spain. In America, while the FBI remained very suspicious of the Spanish veterans, they also became prized recruits for the head of the new OSS Bill Donovan, who recruited individuals such as Bill Aalto as instructors in guerrilla warfare. In Britain, ex-volunteers such as Tom Wintringham played important roles in setting up the Local Defence Volunteers (ie the Home Guard of Dad’s Army fame), while many more joined the armed forces as enlisted men or sometimes officers, although some were rejected for their political beliefs.

About half of the foreign volunteers, though, had nowhere to go from Spain – their governments were either actively hostile or had no desire to take them back. This meant that even as the war entered its final phase, there were still a few thousand foreign volunteers left in Spain. They were lucky in one sense, however – the International Brigades had been concentrated in Catalonia ever since Republican territory had been divided in two by the Nationalists’ Aragon offensive in March-April 1938. This placed them close to the French border, offering a chance at escape if needed.

This prospect soon became a reality. Many of them joined in the final fighting retreat to the French border during the fall of Catalonia in early 1939, crossing into France alongside hundreds of thousands of Republican refugees and soldiers. The French Government didn’t really know what to do with these masses of refugees, and ended up interning them in makeshift concentration camps, mostly in the south of France. There were various schemes to get the volunteers and other refugees out of the camps – Mexico, for instance, was quite willing to take Republican refugees, but arranging passage was expensive, and only a small fraction could be sent over the Atlantic. Controversially, the Soviet Union was unwilling to let ex-volunteers come there, even though most were communists. Most commonly, ex-volunteers languished in French concentration camps until the onset of the Second World War. Many escaped only with the Fall of France and many sought to join Allied armies or to hide, while others ended up in Auschwitz or other Nazi camps. Wherever they went, they tended to become key players in resistance and partisan movements – not only did they have considerable military experience, communists were often in the best position to organise this kind of activity as party structures were designed to operate underground. Spanish veterans, therefore, tended to have the knowledge and connections to be given trust and responsibility in this new context. As such, they crop up time and time again in the history of anti-fascist resistance across Europe – including probably the most famous and successful of them all, Joseph Tito.