Syria has a long history of jihadist activism . The so-called `` Nordic biker war '' of the 1990s saw gang members in Denmark and Sweden attack each other with automatic weapons , grenades , and explosive devices . Denmark has a large immigrant population from the Danish world . four Muslim nationals may have returned from Denmark to Denmark .
Syria has a long history of jihadist activism . Denmark has a large immigrant population from the Danish world . four Muslim nationals may have returned from Denmark to Denmark .