The foreign fighters phenomenon is forcing national governments to devise new methods to deal with emerging threats. Interest of the world's media, experts and policy makers is focused in this aspect primarily on the Islamic State, which is justified by the greater number of people joining its ranks, the scale of its operations, and the number of victims. However, despite the focus on Middle East discourse, there is a profound need for research on the phenomenon of the militants in the Ukrainian-Russian conflict, because in recent years this has become a testing ground for extremely radical groups from more than 50 countries around the world. There is a need to formulate conclusions about the implications for international security raised by the conflict in Ukraine, and to consider carefully whether people from all over the world, who freely took part in this conflict, will become in the near future an unexpected source of radicalisation and new threats. This can be done only through effective understanding of their motivations, national structures, and the ideological relations that exist between them.