GN and HN are subdivided by nations. Two-letter codes are used for nations represented in the current TLD list found online at [https://en.wikipedia.org/wiki/List_of_Internet_top-level_domains#Country_code_top-level_domains Wikipedia]. (This source is preferred as there are a number of competing agencies and standards.) Nations not represented on this list are assigned two character cutter codes. Note that this results in nations being shelved out of strict alphabetical order (sometimes wildly so, as Switzerland uses CH).
New codes will be assigned as needed, using the Internet's Top Level Domain (TLD ) list where possible, and Cutter numbers where not.
Country codes in use include:
Many locations have been part of different countries over the centuries. Items are shelved by the name of the ruling country at the time covered by the item. When works cover a long period, they are shelved under the most recent name, or occasionally under the most common one.
This is a particular challenge for what's now the United Kingdom. While there's a tendency in genealogy to use UK for all areas now included in the country, this is not the case in the field of history. There are many works that pertain only to Scotland, Wales, Ireland, or Northern Ireland. These works are shelved under those names as a means of subdividing the UK. A few works address only the period when the name of the country was England or Great Britain, and those are shelved there.
====State Classifications====