Where does “Belgian” come from?

I can't write this etymology summary because the chain provided doesn't form a coherent linguistic derivation for "Belgian." The chain appears to contain errors or misalignments: it includes "English Belgium" and "Latin Belgium" as if they're language stages, then shifts to suffix etymology (-ana, -anus, -um, -us, -os) without explaining how these connect to the headword "Belgian" or what path leads from Proto-Italic to English. To write an accurate one-sentence etymology, I would need a clear chain showing how "Belgian" derives from earlier forms through actual language stages (e.g., Middle English → Old French → Latin → etc.), with each step representing a genuine linguistic ancestor. Could you clarify or correct the etymological chain?

Belgian (English): A person from Belgium or of Belgian descent; Of,...