Opinion: Putin is calling in favors from Syria and Africa. It’s a dangerous move

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.

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.

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.

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.

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.

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.