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Foreign volunteer fighters can greatly assist Ukraine. But there will be challenges, too.

The Spanish Civil War’s history points to what Ukrainians and the thousands volunteering to fight with them should know

A man who said he wants to join the fight against the Russian army in Ukraine crosses into Ukraine at the border in Medyka, Poland, on Wednesday. (Sean Gallup/Getty Images)

Russia’s invasion of Ukraine has been framed in the West as a key flash point in a wider ideological struggle against militarism and dictatorship. Yet because of the risk of global nuclear war, Western democracies cannot risk direct participation. In these circumstances, the stage has been set for foreign volunteer fighters to play a prominent role in this conflict.

On Feb. 27, Ukrainian President Volodymyr Zelensky announced the creation of an International Legion within the Ukrainian territorial forces, waiving the need for visas, inviting applications through its embassies and publishing step-by-step instructions for potential volunteers. Various foreign governments have indicated that they would look favorably upon such volunteers, and media reports indicate that thousands of people may have already enlisted.

Zelensky’s call for foreign volunteers has precedents, most notably the foreign volunteers who participated in the Spanish Civil War. Their history offers insight into what prospective volunteers — and the world — should expect. While there are practical issues and drawbacks to consider when inviting foreign recruits, such volunteers have made significant contributions in the past, both as fighters and enduring symbols of global solidarity.

In 1936, a fierce civil war raged across Spain and armies fought to control the capital of Madrid. As the elected Republican government fought Francisco Franco’s rebellious Nationalists, a column of foreign volunteers arrived to bolster Madrid’s defenders. Such units became known as International Brigades, eventually encompassing tens of thousands of foreign volunteers fighting to preserve Spain’s fragile yet inspiring democracy. In the words of British communist politician Harry Pollitt, they were “fighting for the democracy not only of Spain, but also of Britain and all of Europe.” All democracies, he asserted, should “support and strengthen” those confronting fascism on their behalf.

Similar rhetoric fuels the global response to today’s crisis, as Ukrainian authorities frame the conflict as an existential threat far beyond Ukraine’s borders — in Zelensky’s words, “If we will fall, you will fall.”

An exceptional number of foreigners volunteered to fight in Spain. Such recruitment was possible not only because of mass sympathy for the Spanish Republican cause, but also because that sympathy was deeply rooted in existing anti-fascist movements and particularly the transnational networks of international communism.

These networks facilitated volunteering on several levels. They ensured prospective volunteers had local points of contact that could help arrange and pay for travel to the war zone. Even more importantly, these networks ensured that recruitment was not taking place among isolated individuals. Rather, the call reached tightknit social groups with shared ideological outlooks, who could decide collectively that volunteering was the right response to the crisis.

This dramatically increased follow-through. So, too, did pan-Hispanism in the case of Spanish-speaking recruits from the Americas, an affinity based on shared language and culture that provided the Spanish Republic with some of its most valuable volunteers. Due to this affinity, these recruits could integrate into the Spanish conflict much more easily than the majority of volunteers who spoke no Spanish, and some who were bilingual acted as vital linguistic and cultural interpreters.

Existing networks facilitated recruitment — but they also played gatekeeper. It quickly became clear that many people who had initially volunteered were unsuitable, due to age, fitness or ideological untrustworthiness. The presence of such volunteers in the conflict zone proved to be a serious drain on resources. Yet sending them home while other volunteers were denied opportunities for leave proved unpopular. As a result, stricter recruitment standards were imposed, including compulsory medical checks, as well as heightened efforts to ensure that volunteers were committed antifascists whose motives and political beliefs were deemed compatible with those of the International Brigades.

Foreign volunteers in Spain came from dozens of countries: across Europe from Ireland to Greece, across the Americas from Canada to Argentina and from as far afield as Ethiopia, New Zealand and China. While individual circumstances varied greatly, most fought to confront and contain fascist aggression in Europe. With both Nazi Germany and fascist Italy actively intervening in the civil war from its earliest days, volunteers hoped that checking their ambitions in Spain would halt their expansionist diplomacy and strengthen European commitments to collective security.

Even with a shared sense of mission and much goodwill, working together still proved challenging. With dozens of languages in regular use, it was difficult for volunteers to coordinate effectively with Spanish military units, and cooperation between the different international units could also be fraught.

While linguistic problems limited the military effectiveness of the volunteers on the battlefield, the simple reality was that even 35,000 foreign recruits could not turn the tide of a conflict fought by hundreds of thousands of soldiers on both sides. The sudden arrivals of volunteers did play a critical role in stiffening the defense of Madrid in 1936-37, but high casualties and dwindling replacements made the International Brigades less effective as the conflict wore on. Up to a quarter of the volunteers died in Spain, the result not just of the intense battles in which they fought, but also their limited experience and training.

Up against the rebellious Spanish army — and its German and Italian allies — Spanish Republican forces and the International Brigades were often outmatched in training and equipment. Most of the remaining International Brigades were withdrawn from Spain just months before Franco’s victory in early 1939. For decades to come, as Franco’s repression silenced most in Spain, the veterans of the International Brigades along with exiled Spanish Republicans helped keep memory and knowledge of the struggle alive.

This history points to a mixed record when it comes to incorporating international volunteers into a military force during war. While medical volunteers and specialist technicians could play particularly valuable roles in Ukraine, having to train large numbers of inexperienced international volunteers for combat could be costly. Focusing on recruiting those with actual military experience and weapons training, or those skilled in medical or technical work needed for the war effort, could make these costs worth it. This is a lesson that may need to be relearned the hard way — Ukrainian authorities said on March 5 that all prospective volunteers were welcome whether they have combat experience or not.

As in Spain, there are questions about ideological gatekeeping. There is a risk, for example, that radical right-wing groups could become recruitment networks. While the far right is hardly unified on the issue of Ukraine, association with any such volunteers may increase the effectiveness of Russian propaganda painting Ukraine as “fascist.” Propaganda and information warfare have been vital in the conflict thus far, and the Ukrainian government can ill afford to recruit foreign fighters without any care for their background or motives.

Perhaps the most useful foreign recruits for Ukraine would be individuals in the Ukrainian diaspora, particularly those with military experience or training. Indeed, on March 5, Ukraine’s Defense Ministry claimed that 66,000 Ukrainian men had returned to fight — an impressive number if accurate. Such volunteers could integrate into both the Ukrainian armed forces and civilian landscape with relative ease. While English probably will emerge as a lingua franca among foreign volunteers today, encounters with local troops, civilians and command structures will still make local language skills vital.

According to historian Nir Arielli, foreign fighters can serve three main purposes: compensating for manpower shortages, filling vital skills gaps and advancing political propaganda. In the short term at least, this final purpose is most pressing. Ukrainian authorities are skillfully rallying world opinion to their side, and the foreign volunteers are now a prominent part of their communication strategy.

Recruits from abroad will create links between the war zone and the wider world, maintaining public investment in events even after the initial shock and spectacle of wartime aggression fades. Without direct foreign intervention — which remains just as unlikely today as it once was in Spain — volunteers from abroad can become important and enduring symbols of international solidarity.