The International Telecommunication Union (https://en.wikipedia.org/wiki/International_Telecommunicatio... the body that governs these things at the international level.

Individual countries implement decisions taken at the ITU through laws and policy. Individual countries take care of enforcement. For instance, in the USA, that would be the FCC.

Each individual country is expected to enforce the rules on its own citizens. The FCC does so here in the US. If I remember right, but am on my phone, there are countries that are not party to the international rules (or don't have agreements with the us? I'm fuzzy) and (us) hams are not supposed to deliberately contact operators in those countries.