That doesn’t sound like 50 countries at all. That sounds like one incredibly disfuncional country.
If your states were like real countries, they could just ban guns, set up border controls, and turn away anyone bringing guns in. But they can’t, so they’re not countries.
Plenty of countries have states with distinct laws and cultures. Canada, Brazil, England, Italy, etc. That doesn’t mean those states are countries.
Sounds like you’re letting US exceptionalism cloud your judgement.