The invasion of Ukraine in 2022 was a pivot in the geopolitical affairs of the region as well as in the mobilization of foreign fighters in general. The war attracted people representing dozens of nations, and these people were inspired either by ideological, humanitarian, or political concerns to participate in the conflict and in many cases without any supervision.
By 2025, the existence and legacy of such foreign fighters have become an important policy problem for Ukraine and the countries of origin of the fighters. These are risks to national security, legal vagueness and increasing reintegration problems.
The composition and scale of foreign fighter involvement
The presence of foreign fighters in Ukraine varied widely between 2022 and 2024 as a first wave of volunteers followed the public call of President Zelensky in February 2022 to volunteer in the International Legion.
Initial recruitment and national origins
In several weeks after the invasion, Ukraine stated that it enlisted over 20,000 foreigners into the International Legion. The fighters came in the countries of Europe, North America, Latin America and some parts of Asia and Africa. Countries including the United Kingdom, United States, Poland, and Georgia to name a few were heavily represented. They had different motives, where some were in support of the sovereignty of Ukraine, others were in opposition to the Russian, and in others, it was on the basis of combat experience.
Some governments such as Canada and Lithuania permitted their citizens to participate without legal consequences and some such as Germany and South Korea gave their citizens warnings or threats of legal action. These national inequalities made the legal environment very disjointed, and it could be difficult to hold people accountable and reintegrate them after the conflict.
Decline and professionalization
By early 2024, the cadres of active foreign fighters had reduced considerably through casualties, disillusionment or voluntary withdrawal. It has been reported that a number of early volunteers went back home months later complaining of disorganization, lack of training and the realities of frontline warfare. The other fighters were former military specialists who became part of more formalized Ukrainian brigades with the shift in the profile from less idealistic volunteers to professional and career fighters.
Intelligence services and other security analysts estimate the current figure of foreign fighters who are still fighting in Ukraine to be around 4,000. Nonetheless, there is a number of highly trained people forming the core of this group and even more concerning is their post-conflict path which continues to pose a growing threat to global counterterrorism agencies.
Security risks and intelligence gaps
The problem of foreign fighters coming home is one that presents a great challenge in terms of national security. Although not all of the returnees are a threat, a small group of them can end up in extremist operations, organized crime and illegal arms trade.
Radicalization and ideological transformation
Although Ukraine as a country is not much viewed as a jihadist theatre, there have been concerns about individuals who may be radicalized through combat. Others came with already existing political scores or right wing affiliations especially those of Europe and the United States. Being exposed to warzones and war methods might strengthen militant ideologies when they go back.
French, Dutch and US security agencies have noted slight but significant increases in online militant rhetoric by people identifying themselves as having combat experience in Ukraine. Such activity has been compared to the situation with the post-Syrian conflict, where sometimes returnees were used as nodes of radicalization or facilitators.
Arms trafficking and battlefield experience
The other danger is due to the spread of battlefield weapons. Although Ukrainian and allied forces are trying to monitor weapons circulation, in particular, the example of military assistance programs, it has been confirmed that there has been smuggling of arms. The 2024 report of Europol cautioned that small arms of Ukraine might appear in black markets in the Balkans and Central Europe, and that there could be criminal syndicates exploiting post-conflict inventories.
The fighters themselves who are trained on urban wars and small-unit tactics can be valuable recruits to the transnational criminal networks. Fighters presenting a possibility of being both enforcers and the brokers of weapons is an issue that makes them a constant menace to the law enforcement.
Legal ambiguity and prosecution gaps
Governments are still struggling with the legal status of foreign fighters in Ukraine. As opposed to jihadist fighting people, whose ties to terrorist organizations can easily lead to prosecution, the participants of the Ukrainian defense cause a more complicated situation.
Contradictory national policies
In some nations, the returnees have been prosecuted because of military service against the rules, countries such as Sweden and South Korea. Other countries, including the United Kingdom and Canada, have been more permissive and multiple returnees have recounted their stories in the media without prosecution. This legal contradiction adds to a patchwork of accountability measures and restricts the international collaboration in tracking of the returnees.
In addition, there are the fighters that have dual citizenship or statelessness, which makes it difficult to follow the jurisdiction and deportation procedures. However, international law does not have a consistent mechanism to deal with such cases that are not associated with established terrorist groups.
The role of mercenary laws
The official statement of Ukraine denies any use of mercenaries, classifying all foreign fighters as regular troops. The legal difference between a volunteer combatant and a mercenary is however unclear particularly when the volunteers are paid or are posted in non-regular units. The ambiguity has led the UN Working Group on the use of Mercenaries to demand a greater clarity in the regulations in its 2025 briefings.
Reintegration challenges and mental health outcomes
The journey back to their homeland of foreign fighters is usually full of individual and institutional challenges. Social reintegration and mental health assistance is meager or absent even in the instances where there is no prosecution.
Stigma and employment barriers
Most of the returnees are subject to suspicion or unfriendliness in their host countries. Others face job challenges especially in those jobs that demand security clearances or government trust. Employers can consider Ukrainian war experience an employer liability, particularly when confirmed or believed to be ideologically oriented.
This stigma in society may seclude the returnees and lead to mental health issues, which add to the trauma of war. The German and Norwegian experience demonstrated that mental health providers are experiencing increased demand with respect to trauma counseling services as a result of the recent returns and services are fragmented and underfunded.
Lack of formal reintegration programs
Most of the foreign fighters do not receive any assistance in reintegrating into society, unlike the military troops who come back through a formalized system. Not many states have specialized support, job training, or mental health services to civilians returning after the foreign wars. This gap leads to more chances of future socio-economic imbalance among this population.
The non-governmental organizations have tried to bridge the gap, but their reach is minimal. The ICRC and OSCE international agencies have come up with reintegration support frameworks, yet their adoption is low based on funding and jurisdiction.
The legacy of foreign fighters in Ukraine is evolving. Their presence since 2022 has reshaped legal and security landscapes, creating ripple effects beyond the battlefield. As governments balance concerns of national security, legal accountability, and humanitarian reintegration, the policy decisions made in 2025 are likely to influence the global handling of foreign combatants in future conflicts.
The question that remains is whether states can build effective mechanisms to support returnees while maintaining security oversight, or whether a new cycle of unmanaged fallout will emerge. The war in Ukraine may eventually end, but the implications of foreign fighter participation are set to reverberate far longer across international borders and domestic policies.
