This is the CodeSystem that contains all the codes in ISO 3166 2 Character Country Codes (http://terminology.hl7.org/CodeSystem/v3-ISO3166-1retired) and ISO 3166 2 Character Country Codes (http://terminology.hl7.org/CodeSystem/v3-ISO3166-1retired). E.g. what you have to deal with if you get resources containing codes in either of them