Raffaello Pantucci has a medium length commentary, with a Syrian focus, as the title suggests 'Foreign fighters – Battle-hardened Europeans return from Syria':http://raffaellopantucci.com/2014/01...rn-from-syria/

He concludes:
Rising numbers of European citizens travelling to fight for Islamist groups in the Syrian civil war increase the domestic terrorism threat as they return home.

European fighters in Syria are from a diverse range of nationalities and ethnicities, with the domestic threat seemingly most elevated in the Balkans, Belgium, and the United Kingdom.

The risk of domestic militant attacks in European countries will rise further should Syria’s civil war continue.