I'm wondering what the correct action the world needs to take, if there even is one. We have a lot of instability caused by fallen governments due to US intervention, which caused ISIS to become what it is now. Let's say pretty much the U.N. (lol) all come together to send troops into Syria and other problem areas to wipe out ISIS and are successful in doing so... what then? It wouldn't take very long for another extremist group to rise up in power due to lack of a strong, structured government in those areas.
A lot of these governments were unstable, that is why they needed to use violence to justify their existence.
There is some real science behind this. Bernie oversimplified it but people who strawman and say "Icebergs cause terrorism" or something are being ignorant.