In all some 30,000 foreigners have joined extremist militias in Syria and Iraq. 5,000 are believed to come from the EU, mainly from France, Britain, Belgium and Germany.
118 jihadi fighters are believed to have already returned to Belgium. A report by The Soufan Group repeatedly refers to the Brussels suburb of Molenbeek as a focus for the radicalisation of youngsters. Molenbeek has also been linked to the Paris attacks.
Most but not all jihadi fighters from Belgium are of North African descent. Some never integrated into mainstream Belgian society. Many are petty criminals who have served time in a Belgian jail.
The report suggests that extremist groups like IS offer youngsters with few prospects a new future, a new identity, a purpose in life and the prospect of adventure. Radicalisation occurs within weeks and often without friends and family noticing.