Per Wikipedia Mexico, Honduras, and Guatemala also have constitutional protections of varying strength.
They do, but in practice they don't. Many European countries which don't have a right to bear arms still manage to have better gun laws than those three Latin American countries (and I should add, a number of American states).
The other countries haven't become provinces of other less Democratic countries thanks to America's protection.
Other countries still have armies and soldiers without having armed civilian populations. And America could do this too if they wanted to.