Given your use case, the term administrative division, or one of its synonyms, might be what you are looking for. As it is explained on Wikipedia,
Administrative divisions (also administrative units, administrative regions, subnational entities, or constituent states, as well as many similar generic terms) are geographical areas into which a particular independent sovereign state is divided. Such a unit usually has an administrative authority with the power to take administrative or policy decisions for its area.
One could object to this answer, since the definition given by this Wikipedia page pertains only to subdivisions of countries and you have explicitly given both countries (Estonia) and supranational unions (the EU) as examples.
However, "administrative division" is usually qualified by an adjective like "first-level" or "second-level." An example of this usage is in Wikipedia's "List of administrative divisions by country" which shows this scheme applied to each country. You'll notice that these qualifying adjectives are defined relative to an implied zeroth-level, which would be the country. The specifications of one particular dataset even explicitly names national-level administrative boundaries as "Level 0."
I think this is a salient term for your database usage since it already has an established usage in geographical datasets and databases. For example, the GIS company Esri has a "World Administrative Divisions" dataset, and the CIA World Factbook provides a list of administrative divisions.
World Administrative Divisions provides a detailed basemap layer for the country first-level administrative divisions of the world as they existed in January 2020.
This entry generally gives the numbers, designatory terms, and first-order administrative divisions as approved by the US Board on Geographic Names (BGN).
For your use case, you might have to define the "levels" differently than existing examples, because your "zeroth-level" might be supranational unions like the EU and your "first-level" might be individual countries, and so on and so forth.