I reckon they can move to the west as well, if they wanted to and will have to fight a tough battle against countries in battle if they try to take over and will lead to lives lost. I think they had good motives in the early days but, overtime like the Naxalites in India resorted to violence and slaughter to get what they want and take it by force if they have to. So they will do that if they have to and may do it, and rule over by being a terrorist and use a iron fist to rule over the weak and slay those who oppose them which has happened.
I don't think ISIS poses a significant threat to the West at this point in time.Sure they have managed to struck terror in the hearts and minds of those who have managed to catch a glimpse of their atrocities on line but this only ends there.They don't possess the network required to infiltrate foreign countries physically as of now since they are being closely monitored.But time will definitely tell.
Not conventionally. But they will be able to inflict economic losses to the west [through military spending] and there is a high risk of terrorist attacks being planned and carried out by the group or affiliates in the West. Considering how many fighters are joining their ranks from abroad, I can see the last point being a very real - and very scary possibility.
Terrorists are a threat to the entire human population. The west doesn't have the monopoly of threats. Even an indigenous person living on the mountains will feel threatened by the mere presence of terrorists who tend to defile their resources and drive them away from their own land. The point is, terrorists don't care whether you're western, eastern, southern or someone from the poles. If you happen to be their target, then what bad luck. They don't have a clear ideology. They use religion as an excuse to wreak havoc. They're just there to disrupt what little peace we have here on earth.
I would say ISIS are indeed a threat to the West. OK, there is much tighter monitoring right now but we already know that ISIS sympathizers can be found all over the world. Internet recruitment will also increase so they can gain volunteers in the countries which they wish to target.
I think people have misinterpreted the threat posed by ISIS. ISIS don't necessarily have the military power to wage war with the west but what they have is influence. They are influencing people from the West to carry out attacks within their own country.
I don't think it can be crushed. Look at Iraq/Afghanistan. Nothing has been crushed there - in fact, it's only made things worse and allowed for ISIS to exist. The strategy should be on making it difficult for any terrorist groups to gain influence - and that requires the proper foreign policy and ability to exert positive influence wherever possible.