2. Background: Overview of FTF Dynamics, Challenges and Responses The starting point for many analyses of what is often referred to as the “FTF-phenomenon” is to note that it is, in many respects, not new. Foreign fighters have been a staple feature of many if not most armed conflicts, international and non-international, for many decades.14 However, it is only in recent years, with the influx of FTFs to Syria and Iraq, and increasingly their return to states of origin, previous residence, or onward travel to third states, that the issue has become a matter of intense international concern. Understanding the nature of the FTF problem – the motivation of those engaged in FTF-related travel and return, and the threat it represents – is a necessary pre-requisite to formulating effective strategies of prevention and response. While an in-depth exploration of its manifestations goes beyond the scope of this document, a few background facts from a growing body of research and literature are worth highlighting. These should inform discussions on effective and targeted legal and policy responses. Foreign Fighters Today Available information suggests that FTFs who travelled to and actively engaged with the so-called “Islamic State” in Iraq and the Levant (ISIL), Al-Qaida and associated groups in Iraq, Syria and other countries – such as Afghanistan, Yemen, Libya, Pakistan and Somalia – came from an estimated 110 states around the globe. While estimates are by their very nature unreliable, linked in part to definitional problems, it has been suggested that more than 40,000 foreign terrorist fighters had travelled to just Iraq and Syria alone as of late 2017.15 Those who travelled from European states to the conflict 14  Reference is often made to the large number of foreign fighters who fled to the Spanish civil war, to oppose Soviet occupation of Afghanistan, or to participate in the conflict in the former Yugoslavia, though a growing body of analysis makes clear that the practice goes far beyond these renowned examples. See, for example: M. Flores, “Foreign Fighters Involvement in National and International Wars: A Historical Survey”, in Andrea de Guttry, Francesca Capone and Christophe Paulussen (eds.), Foreign Fighters under International Law and Beyond (The Hague: T.M.C. Asser Press, 2016), pp. 27-48 (hereafter FFILB). See also: D. Malet, “The European Experience with Foreign Fighters and Returnees”, in T. Renard and R. Coolsaet (eds.), “Returnees: who are they, why are they (not) coming back and how should we deal with them? Assessing policies on returning foreign terrorist fighters in Belgium, Germany and the Netherlands”, Egmont Institute, Brussels, February 2018, pp. 7-9, <www.egmontinstitute.be/content/uploads/2018/02/egmont.papers.101_online_v1-3.pdf?type=pdf>, (hereafter, T. Renard and R. Coolsaet (eds), “Returnees: who are they, why are they (not) coming back and how should we deal with them?”, Egmont Institute). 15  See: “Greater Cooperation Needed to Tackle Danger Posed by Returning Foreign Fighters, Head of Counter‑Terrorism Office Tells Security Council”, United Nations, 29 November 2017, <www.un.org/press/ en/2017/sc13097.doc.htm>. Guidelines for Addressing the Threats and Challenges of “Foreign Terrorist Fighters” 11