This is the CodeSystem that contains all the codes in ISO 3166 3 Character Country Codes (http://terminology.hl7.org/CodeSystem/v3-ISO3166-2retired) and ISO 3166 3 Character Country Codes (http://terminology.hl7.org/CodeSystem/v3-ISO3166-2retired). E.g. what you have to deal with if you get resources containing codes in either of them