Islamic State: What is the attraction for young Europeans?
The flow of recruits, both fighters and families, leaving their homes in Europe to live under so-called Islamic State (IS) rule in Raqqa in Syria has slowed dramatically.
It reached its peak in 2013-14, when it was far easier for jihadists to cross the 822km-long (510-mile) Turkey-Syria border, when IS propaganda on social media went largely unchallenged, and when IS was on a roll militarily, seizing ever more territory across northern Syria and north-western Iraq.
While all three of those factors have now changed to the detriment of IS, the underlying factors propelling young Britons and Europeans towards joining the group have not gone away. So what are they?
IS has been phenomenally successful in exploiting a sense of alienation and a "failure to belong" among many young European Muslims.
Many recruits have felt alienated from their families, on the one hand, and from the wider societies they live in, on the other.
Here, the internet has played a major role. Teenagers still living at home will spend large amounts of time shut away in their rooms online.
Parents often have little or no idea about who their son or daughter is communicating with, and by the time they realise they are being radicalised by someone it is often too late.
There have been many cases of concerned families reporting their suspicions to the authorities, and an ever-increasing number of cases are being referred to the UK government's Channel programme, which focuses on providing support to those identified as being vulnerable to radicalisation.
Just as serious as alienation from the family is alienation from society.
IS propaganda aims to convince potential recruits that their loyalty belongs not to their country of residence but to the IS-declared "caliphate", and that to vote in Western elections, pay Western taxes or to serve Western governments in any way is "haram" (forbidden).
Their message is that life in the West is a waste of time and that "hijra" (emigration) to "dar al-Islam" (the realm of Islam), lands under Muslim rule where Sharia prevails, is the duty of all Muslims.
For someone deeply unhappy with their life in the UK, won over by the mirage of some distant society ruled fairly according to God's laws and not man's, this can be an attractive proposition.
Key to delivering this message is IS's adept use of persuasive, charismatic figures.
Statistics show that in most cases people are persuaded to join the IS cause by their peers.
This can be an older brother who has already gone out to Syria and tells them how perfect life is out there, a classmate, or even a stranger encountered online who uses a nom de guerre like "Abu Abdullah al-Britani".
A former IS recruit I interviewed in a Jordanian prison in 2015 told me how his best friend from school went to Syria, fought for IS and persuaded him over the phone to join him.
He did, but disliked and deserted after just two weeks.
Unfortunately for him, when he returned to Jordan the authorities gave him a mandatory five-year prison sentence, hardly an incentive for others to have second thoughts.
Against the lure of seemingly "heroic" IS fighters attracting others online to their cause, European government and community leaders were initially slow to respond.
Imams and other Muslim community leaders have been appalled at seeing their co-religionists drawn away into such a violent, world-hating cult.
They have written public letters condemning IS, issued sermons at Friday prayers and reported to the police individuals showing signs of radical behaviour.
Yet in terms of charisma these religious and community leaders have little influence over young people, at least not compared to the glamour attached to some of the fighters, brandishing Kalashnikovs and bandoliers, and recruiters churning out a constant stream of slick propaganda from Raqqa and Mosul.
Researchers have concluded that one of the principal driving factors behind IS recruitment in Europe is the idea that the person is somehow serving a greater or higher cause, in this case something presented as "the nobility of jihad (holy war)".
For someone whose life in the West appeared to lack meaning, purpose or dignity this can quickly resonate. A young person connecting with a charismatic fighter skyping from Syria can therefore be persuaded to give up his life here in a matter of a few weeks.
For some brainwashed young men, the notion of being somehow "sent on an important mission", even something as self-destructive as blowing yourself up at an Iraqi checkpoint, can give them the illusion of being selected for some elite role with a grand purpose.
The slick messaging and skilful - albeit sick - use of graphics, cinematography, and extreme, voyeuristic violence has certainly increased the appeal of IS among certain people, many of them with criminal backgrounds.
The sadistic forms of execution meted out to IS's enemies, predominantly other Muslims, serve in turn to pull in more individuals with psychopathic tendencies.
Barbaric cruelties abhorrent to most people, like the enslavement and rape of children as young as 12 from among captured communities, are either ignored or explained away with various religious justifications and quotes from centuries-old texts.
In recent months, IS has toned down some of its more graphic imagery, perhaps aware that it is repellent to so many people, emphasising instead its strategic view of itself and its perception that despite the many military setbacks now being suffered, its eventual triumph is somehow inevitable.
In the UK, the government has been slow to appreciate the uphill battle it is fighting in the messaging space. It is now beginning to push back with so-called "counter-messaging".
But ultimately, until large numbers of people come back from IS territory and tell the world "Don't do it, we made a terrible mistake", IS's messaging is likely to continue to resonate with certain young men and women across Europe.