Or even the Roman Empire itself.

> an empire is a state where the core ruling population exercises control and extracts resources from a periphery which is composed of people other than the core group

By definition, doesn't the later Roman Empire cease being an "empire" as there isn't really a "core" population anymore outside of some vague multi-ethnic military aristocracy.

Sure, Rome had a few lingering privileges and prestige, but little in the way of direct power. And certainly, the post-crisis Empire didn't exist to siphon resources on their behalf. Heck, pretty much as soon as the 3rd century crisis ended Italy itself lost most of its special status and more or less just became yet another province.

And once that was gone, they weren't really replaced by anyone except the imperial bureaucracy and aristocracy itself. So who are the "core" people here, because if "an aristocracy" is enough to count, then who the heck isn't an empire under this definition?

Maybe it's enough that they began as an empire under this definition. Or maybe Devereaux is fine with the stereotypical Empire losing its status as an empire long before losing its territory and power. Or perhaps would have some counterargument at hand if he happened to read this. Who knows.