A quick glance of the military capabilities of Ukraine and Russia shows a David versus Goliath battle. On paper, Russia’s armed forced forces have thousands more troops, weapons and vehicles – with a staggering military budget to boot. On the ground it’s a different story, where Russia has met fierce resistance from Ukraine’s vastly outnumbered military. In the first two weeks of the invasion, Ukraine’s President Volodymyr Zelensky’s call for foreign volunteers to bolster his country’s defense saw more than 20,000 people from 52 countries put their hands up, according to government officials. The influx of foreign fighters into Ukraine has been met with sympathy in many Western states, where citizens and even political leaders, have expressed support for those fighting Russia’s invasion. Some leaders, such as United Kingdom Foreign Secretary Liz Truss, or Danish Prime Minister Mette Frederiksen, even encouraged civilians to travel. Not to be outdone, President Vladimir Putin last week also called for foreign reinforcements – many of the applicants reportedly coming from the Middle East and Africa, where Russia has invested in bolstering governments and military actors, who are now in position to repay. Russia has called in favors from ally Syria – where Putin’s troops backed government forces in the country’s long civil war – claiming nearly 16,000 volunteers are ready to fight on their side. And in Africa, Russia has sought to cultivate support in places like the Central African Republic, where Russian advisers and private military contractors have bolstered the authority of the government in Bangui. Add in widespread reports of the increased presence in Ukraine of the Wagner Group, a Russian private military company whose owner is reportedly close to Putin, and which is apparently offering starting salaries of $2,000 per month for all nationals (except Georgia), and the picture of foreign fighters in the war is going to get more complicated. And dangerous. African states have been divided over Russia’s invasion. During a historic vote earlier this month on Ukraine in the United Nations General Assembly, 24 African countries refrained from condemning Russia’s invasion; 16 abstained, seven didn’t vote at all and one voted against. For many states, longstanding relationships with Russia or historical commitments to the Non-Aligned Movement shape their response. Others see in Russia an anti-Western ally and in the case of Central African Republic for example, one that prevented a rebel onslaught. In Uganda, the President’s son, Lt. Gen. Muhoozi Kainerugaba, widely rumored to be his successor, said: “The majority of mankind (that are non-white) support Russia’s stand in Ukraine.” For good measure, he added, “Putin is absolutely right!” It is notable that countries where the Wagner Group has been active – including Mozambique, Central African Republic, Mali – all abstained from voting against Russia at the UN. For some, fighting in Russia will provide an opportunity to challenge the post-colonial era dominated by the West; for others it will provide a valuable income and combat opportunities. The experience of Libya however, has shown that the return of fighters with military experience has prompted instability and violence in the region. For over a decade, Russia has shielded Syria in the Security Council and flooded it with weapons, personnel, and operational support. Russia’s longstanding support to Syrian President Bashar al-Assad allowed him a brutal testing ground for weapons, tactics and recruitment. In return, on the first day of the invasion, Putin reportedly called Assad who told him that, “Western nations bear responsibility for the chaos and bloodshed.” It is unsurprising that Syrian volunteers are now being recruited, with US assessments indicating their experience in urban combat will be of particular value to Russia as it regroups for more assaults on Ukraine’s cities. Over the past decade, the term foreign fighters has conjured up images of another war in the Middle East, where nearly 40,000 people traveled to Syria and Iraq. The adversary for many was a brutal dictator; yet the ally was a UN-designated transnational terrorist group. This is not that war. Russia’s invasion of Ukraine has prompted the establishment of a Ukrainian Foreign Legion, under government control. Western interest is likely to remain high in supporting Ukrainian forces in fending off invasion and occupation. Statements from volunteers have overwhelmingly indicated interest in bolstering a sovereign democratic government in the face of unprovoked aggression. But should the current war morph into a longer-term insurgency, the scene for foreign fighters and supporters can change, with some sharpening ideological or political views or favoring extremist narratives. Moreover, in order to meet their obligations under Security Council counterterrorism resolutions, states have adopted measures, such as criminalizing travel to conflict zones or material support to terrorism – without actually defining terrorism – that can complicate the picture. It means there could be tensions between actions deemed permissible in conflict zones and what can be characterized as terrorism. As states confronted the challenges of travelers bound for Islamic State in Syria and Iraq, they unified around a set of sweeping and binding UN Security Council resolutions in order to address the phenomenon of what they termed foreign terrorist fighters – those traveling with the intent to support a designated terrorist group. In 2014 and 2017, the Security Council adopted two binding resolutions as states grappled with the prospect of foreigners traveling to conflict zones and returnees. These highlighted the need for a package of responses that included prosecution, rehabilitation, and reintegration. That terminology could further complicate the outlook for volunteer fighters in Ukraine. These measures were adopted when there was unparalleled international consensus about the status of ISIS and when terrorism was one topic where all five permanent members of the Council could agree, in large part. But now that these measures are on the books, there are risks individuals traveling to Ukraine could run afoul of them, or that the lack of clarity about some counterterrorism laws could endanger them in situations of armed conflict. While initial intentions from many traveling from the West have been overwhelmingly humanitarian and in support of a beleaguered sovereign, democratic government under attack, motivations can change over time. The influx of more diverse actors, could also cloud the legal minefield and prompt potential tensions between counterterrorism and humanitarian law. Already Russia has indicated they would consider foreigners traveling to fight in Ukraine as mercenaries, and that they would not be considered combatants protected by international humanitarian law. As long as volunteers are traveling to join the officially established foreign legion, and remain under responsible military command while in Ukraine, there may be some measures of legal protection. But individuals may be affected by exposure to atrocities, or recruited by groups with diverse ideological goals, particularly if they are not accepted into the foreign legion. Sympathizers abroad may grow increasingly frustrated with their own countries’ responses and opt for more violent forms of political expression at home. During previous flows, returnees have not perpetrated harm in large numbers. But many will return battle-hardened with combat experience and new transnational networks that may be activated for other causes, and those that wish to do harm may be more capable of doing so. But there are two things we can do now. States need to review their counterterrorism legislation and clarify when and where these do – or don’t – apply with regard to Ukraine. With the fragmentation of consensus in the Security Council and the end of a post-9/11 era agreement on countering terrorism together, the Council may no longer be the place to determine what a collective international response looks like. In the geopolitical fallout of the war in Ukraine, there will be an urgent need to reassess the roles and contributions of multilateral counterterrorism efforts – like the vast bureaucratic architectures at the United Nations, Global Counterterrorism Forum and other intergovernmental bodies developed in the wake of the 9/11 era. Nonetheless, the flow of volunteers to Ukraine and Russia, increases the need for international cooperation among all states to ensure the safety of their citizens – and plan for their safe return.