And in more than 30 countries around the world, a rag-tag assortment of armed groups have pledged allegiance to the ' caliph' or Islamic State leader. That spells trouble for years to come.
The messaging that motivates and mobilises people to fight for their vision of Islam is spread in a multitude of ways, but especially through social media.
Radical sympathisers have shown that social media platforms can provide spaces for effective recruitment, moving inquirers and disaffected youth especially from interest to action. Doing so doesn' t require much specialised equipment - a laptop and know-how will do.
It's easy, therefore, for followers of IS-type Islam to exert influence online, and that' s true even if the digital services they use are wise to their tactics and move quickly to shut down Islamist-linked accounts.
For example, the electronic jihadis practice what' s known as ' swarmcasting' . Say someone posts a beheading video on Twitter. The strategy is to have as many sympathisers as possible download it before Twitter closes the account. In one case, nearly 60,000 people had downloaded material before the account was shut.
The downloaders then become ' disseminators' - sharing the video with their own networks so the distribution of the video shape-shifts like a flock of birds or a swarm of bees, constantly forming and re-forming.
The jihadis are alert to the attempts to stifle their online efforts, and have learned to use apps such as Telegram, whose messages are heavily encrypted and can self-destruct. They' ve produced a guide on how to frustrate those wanting to disrupt their communication. Getting into the inner circles of contact can be a matter of recommendations from trusted radicals who usher potential recruits through progressively closer levels of engagement.
We should study extremism in all its forms, including that represented by Islamic State. And we should engage with those whose views and values are different.
These recruits might be motivated by more than just a desire to fight.
Reportedly an IS fighter captured by Kurdish Peshmerga troops told his captors: "Kill me now - I have to be in heaven by 4pm." He wanted to reach paradise in time for a religious ceremony. That' s the power of a religious ideology which, in its extremes, justifies everything from modern slavery to crucifixions, to brutal treatment of enemies including mass murders and attacks on civilians in Europe and America.
What does all this mean for New Zealand?
We know (because the Prime Minister has told us) that our security services keep a watchful eye on some individuals in our society. Our watchdogs are alert to online as well as other forms of communication. Does that mean the rest of us can relax?
While it doesn' t mean we should look at Muslim neighbours, including immigrants, with suspicion or fear, we do need to note what's happening in the world. Innocent people have been slaughtered in places as diverse as shopping malls, cinemas and transport stations simply because their murderers saw them as deserving of death.
The challenge is not to blame other Muslims for these crimes - we largely share the same aspirations: the best possible life now and a positive future for their children.
We should study extremism in all its forms, including that represented by Islamic State. And we should engage with those whose views and values are different.
Understanding may not bring acceptance of the other's point of view - but it might help take the sting out of the bigotry and disillusionment that drives the ideologies sitting at the far end of the spectrum.
Dr Chris Galloway is the head of Massey University’s public relations programme. He has researched the communication and recruitment methods employed by IS.
