Why nobody invades the USA?

Here's the top five [gun ownership rates] : US at 89 small arms per 100 people, Yemen at 55 (a gun-&-knife-toting culture without peer in the uncivilized world, but we still kicks their asses!), Switzerland at 46 (who knew?), Finland at 45 (still expecting the Russians), and Serbia at 38 (just got in the habit, I guess).

But they have to protect themselves against the Islamist, terrorist, Marxist revolutionary who just got elected president, right? And a hell of a lot of hunting.