The answer is no, but it's a legit reason to worry. ISIS aren't technically a country (caliphate- whatever) and while they've a lot of soldiers on the ground, they've not really enough to start an outright war. They've a lot of resources, granted, but again, not enough for an extended, entrenched war on multiple fronts. Most importantly, they're not (as yet) seen as being their own government in the Middle East by their Middle Eastern neighbours. It's difficult to rally your allies for a World War when you've not even succeeded in taking over the country you're fighting the civil war in.
If ISIS does somehow manage to get caught up in a World War, it'd be with Putin's support and string pulling, and they'd be at best a small medium cog in a very complex and large machine. And Putin and his Russia are very, very frightening right now. Putin has all the signs of wanting to bring the USSR back and there's a pretty decent chance he could pull it off in only a few years. The major problem is that while no one wants the USSR to make a comeback, Russia supplies around 40% of the European Union's fossil fuels. It's effectively got the genitals of 250 million people in the palm of its hand, and Russia has a very tight grip. So if Russia cuts off the supply of oil, the world must rely very, very heavily on the rest of their suppliers. The vast majority of which are countries in the Middle East.
Whoops.
But while Russia's sniping at the EU and the USA is frightening, there's another country that looks set to get involved in the mess, and this one is terrifying. War between Russia and USA and the EU, you need to hoard tinned food and water, get all your cultural treasures underground where the bombs can't get to them, be ready to rake the skies with missiles if so much as a large bird flies ahead, and build your own miniature radiation-proof bunker at the bottom of the garden. If this other country gets stroppy, however, there's going to be more than a few surrounding countries who'll surrender absolutely without hesitation.
So what can be more frightening than a fuck huge war with the USA and the EU against Russia and the Arabs?
It's a country that even fucking Napoleon was frightened of.
It's the sleeping dragon. And it's not asleep anymore.
It's China.
And it's stretching out its claws right now.
If WW3 breaks out any time soon, chances are good that two main sides won't be the EU, the USA and their allies against Russia and its allies. Instead it'll be China coercing its terrified neighbours to join them against Russia and anywhere else that pisses it off. And that's when the entire world will burn.
