If the free world truly united, this threat could be met and defeated. It's a matter of will, not capability. I don't think vacillation (caused by lack of will) will necessarily result in the utter destruction of western civilization because at some point, we will be forced to wage an all-out war of survival against Islam (might as well throw Islam into the mix for it is spawning the terrorists). I believe it will be won but it will be much more costly than if the lessons of WWII had been learned.
You're thinking Star Wars. In real life, countries stay out of expensive wars until they are dragged in. And even then, they put in the absolute minimum they can, on the premise that somebody else could better afford to contribute to the cause.
The likelihood is very low
Let us rent some of those ore ships that move between China and Brazil, draft all those welfare and send them over with rifles and MRE’s. Millions of them.
If they refuse, no more benefits.
Their mission is to eliminate Islam.