http://www.brookings.edu/~/media/res...d%20%20web.pdf

Be Afraid.
Be A Little Afraid:
The Threat of Terrorism from
Western Foreign Fighters in Syria
and Iraq

This paper first lays out the standard schematic view
of how and why some foreign fighters become dangerous
terrorists, drawing on the Afghanistan experience
in the 1980s to illustrate the arguments. The
second section discusses why many seasoned observers
believe the Syria conflict is likely to be particularly
dangerous. In the third section, we examine
why terrorism in Europe and the United States was
less than expected from previous jihads such as Iraq,
again drawing implications and lessons specific to
Syria, as well as examining factors unique to the Syrian
conflict itself. The fourth and final section identifies
policy implications and recommendations.