The FIPS 10-4 standard, Countries, Dependencies, Areas of Special Sovereignty, and Their Principal Administrative Divisions, was a list of two-letter country codes that were used by the U.S. Government for geographical data processing in many publications, such as the CIA World Factbook.
3 (November 2003) and as DIA 65-18 (Defense Intelligence Agency, 1994, "Geopolitical Data Elements and Related Features").
[1] The National Geospatial-Intelligence Agency continued to maintain the FIPS 10-4 codes in an informal document titled "Geopolitical Entities and Codes" (GEC) until December 31, 2014,[2][3] retiring the GEC on March 31, 2015.
[4] On January 23, 2013, the U.S. Department of Defense released the first edition of "Geopolitical Entities, Names and Codes" (GENC), a U.S. federal government profile of ISO 3166-1 and ISO 3166-2.
GENC is designed to be compatible with ISO 3166 but reflect U.S. government diplomatic recognition and naming decisions by the U.S. Board on Geographic Names; it is intended to be the basis for a future U.S. national profile of the ISO standards.