Hitler chose not to invade Switzerland for several reasons.
Switzerland is small and mountainous, and of course the Swiss Army being well trained and armed as well was a factor. But Switzerland also provided a way to launder money and artworks. Hitler had declared modern art decadent, but it was also valuable, and rather than destroy it, it was sold through Swiss dealers.
The gun violence rate in the US is 3.6 greater than the rate in Switzerland. The Swiss tend to focus more on rifles and shotguns, while Americans concentrate more on pistols.
Guns are registered in Switzerland, but not in the US.