> Isn't that the law in most (all?) states now in USA, that you need a license to possess a gun legally (ie need to be an authorised person)?

Not really. Only a few states have FOID or FID license requirements:

https://en.wikipedia.org/wiki/Gun_laws_in_the_United_States_...

You might be thinking of license to _carry_ which every state has, though some of have been making progress in removing that requirement as well. https://en.wikipedia.org/wiki/Constitutional_carry