[dukeofharen]

If I'm not mistaken, ICANN uses the ISO 3166-1 alpha-2 codes as country TLD's, so in a sense the UN indirectly specifies the rules for ICANN. https://en.wikipedia.org/wiki/ISO_3166-1_alpha-2

[gbxyz]

The UN publishes a list of recognised member states. ISO maintains a list of codes. IANA uses that list to determine whether a country code TLD is valid. But that's the extent of the UN's involvement in the governance of the root zone.

[midasuni]

There are plenty of TLDs for areas which aren’t countries, whcih don’t claim to be counties, which nobody recognises as countries. .gg and .gu for example.