Well NATO works both ways, and we’ve seen recently what happens if russia decides to walk into a non-NATO country.
If russia walks into the USA then NATO (probably renamed to the European Defence something) will be sitting back going “hey, sucks to be you. Shame you’re not in a mutual defence pact or something.”
Not a cryptographic expert by any means but maybe something like this would work. This’d be implemented in common places people shop: supermarkets for instance. You’d go up to customer service and show your ID for visual confirmation only; no records can be created. In return the service rep would give you a list of randomised GUIDs against which the only permissible record can be “has been taken”. Each time you need to prove your age you’d feed in one of those GUIDs.