Is ISIS a threat to the whole world which has to be stopped immediately or it's just a local Arab conflict? I think that ISIS is just yet another word for Islamic fundamentalism and Arab nationalism. Even if we get rid of ISIS there will be still people wanting to unite all Arab or Muslim states into a single country. Is there any way to prevent it from spreading around or it would be better just to forget about the region?
They aren't a threat in the sense that everyone from LA to Tokyo is going to wake up one morning to find Muslims parachuting down from the sky to impose Sharia law on everyone. But consider a situation in which, say, the Assad regime capitulates and ISIS overruns Syria. Suppose Russia begins asking itself, "Who lost Syria?" and decides it hasn't been aggressive enough in foreign affairs - so they start trying to annex more things in Eastern Europe and possibly the Caucasus. Suppose an emboldened Islamic State attacks Iran directly. There are plenty of ways for things to get broken without ISIS breaking them itself.
ISIS is an Islamist group but it is not the be-all-end-all of Islamism. Al-Qaeda has condemned ISIS. Saudi Arabia is, by definition, an Islamic fundamentalist theocracy and they obviously do not like ISIS.
Arab nationalism is a completely separate (and largely defunct) ideology that isn't really compatible with Islamism. Islamism is somewhat like Marxism in that it believes nationalism is largely a false distraction from what "really matters." For Marxists, class was what really mattered. For Islamists, religion is the important thing. National boundaries divide the "ummah" (the community of believers in Islam). Less than half of the "ummah" lives in the Arabic-speaking world. And Arab nationalism requires the accommodation of Christians (which is part of the reason Christians played such a major role in promoting it).
