Beware: Arbitrary definitions to follow
Technically speaking the words kingdom and realm are interchangeable. As I work on these posts on lost kingdoms it occurred to me that I have a few planned posts on entities that really fall in a gray zone, either because we have little proof they existed or because their location is unfixed. So what is the right term for them? Proto-kingdom? Pseudo-kingdom? Principality is no better. District really isn’t either since district implies a regularized grid or plan. Petty kingdom is just weird and one of the entities I’ll be writing about wasn’t petty, if it existed. So realm is the term I’ve decided on.
A realm refers to an area ruled by a king, perhaps passed on to his successor, or not. There were certainly many transient realms. Indeed, one of the differences between realms and kingdoms are that kingdoms tend to remain together even when the whole dynasty changes.
A kingdom may be absorbed into a larger kingdom, but even then it tends to retain its organizational structure and identity. Lindsey remained a distinct unit even when completely assumed by either Northumbria or Mercia. Its still a district or county today.
Some realms had a core kingdom in addition to a swollen tribute area. “Northumbria” is a realm until 679 when Ecgfrith assumed direct rule over Deira for the final time and the southern border was set by arbitration. Bernicia is the core kingdom of the realm of Northumbria. Even then the term Northumbria probably didn’t consistently exist. It king would have simply been called King of the Angles/English in the north.
So comments or suggestions?