Except American's aren't the brightest anyways, and they seem to suffer from a sort of Hubris where they believe they're superiority, and capability is nearly empowered by God himself. I've yet to hear a single person doubt this propaganda, this everyone is safe because we're awesomer then everyone else type of thinking.
...And perhaps they're right. Then again, far too many battles have been lost by hubris in the history of war, and the belief in an unstoppable their military.
Let me be frank, it's not a question of IF America will fall, it's a question of when. We could be brought down by a new world empire, or whimper away from economic collapse, or it could be some random crazy fat Korean name Jong-Un who fires a lucky shot, with a half-baked nuke, and gets lucky. The odds of winning the lotto, or being struck by lightning are astronomical, but yet it happens.
However, Korean's don't have to master missle technology, nor nuclear technology themselves. They simply need to inherit it from another country. Never doubt the possibility of a cold-war nuke (which there are thousands unaccounted for) landing in the hands of some crazy guy with a bad hair-cut.
Even if he can't, even if he doesn't, even if these are the same threats people say Korea has been making for decades, the threat of Nuclear war is not something we should ever consider there being a zero chance of, ask my friend Goliath about that.