US the terrorists would have to kill about 30,000,000 of us and show that they were willing to do the same to the remainder. All they can do is piss us off, they cannot possibly defeat us.

Go read history. Read what happens to transients during war. This is what "concentration camps" or "internment camps" were invented to do, to concentrate the transients. And during an actual war moving across borders becomes very very difficult.

And I expect that ISIS will be similarly popular in a lot of places. Leaders who promise morality and victory tend to popular all over the world.

But how the Caliphate was created has little to do with whether or not there is a war. The US supported Islamic forces against the Russians in Afghanistan. That didn't stop the US from tipping their government over.