Why dissolved countries still need codes
When a country ceases to exist, the data tagged with its old code does not vanish. Banking records, shipping manifests, census archives, and historical datasets all keep referencing the USSR, Yugoslavia, or East Germany long after those states were gone. ISO 3166-3 gives each defunct country a stable code so that history stays unambiguous.
How it works
Every ISO 3166-3 entry is a four-letter code. The first two letters are the country’s former ISO 3166-1 alpha-2 code; the last two letters describe what happened to it:
SUHH = SU (former USSR) + HH (no single successor — dissolved)
CSXX = CS (Serbia & Montenegro) + XX (split, codes not yet final)
BUMM = BU (Burma) + MM (became Myanmar)
DDDE = DD (East Germany) + DE (merged into Germany)A successor’s alpha-2 code (like MM or DE) means the territory became, or merged into, that country. HH marks a dissolution into several states with no single heir, and AA marks a pure name change.
Tips and notes
When migrating old records, map each ISO 3166-3 code to its modern successor before aggregating — otherwise you will double-count or lose territories. Watch out for codes that have been reused: CS once meant Czechoslovakia and later Serbia and Montenegro, which is exactly the kind of collision ISO 3166-3’s four-letter scheme is designed to disambiguate. The list above sorts alphabetically and is searchable by name or by any of the old or new codes.