Landholders who could be Belgians? (8)
I believe the answer is:
liegemen
'landholders' is the definition.
'be belgians?' is the wordplay.
I cannot quite see how this works, but
'be' could be 'lie' (lying is a kind of being) and 'lie' is present in the answer.
This may be the basis of clue (or it may be nonsense).
'who could' is the link.
(Other definitions for liegemen that I've seen before include "Feudal vassals" , "subjects" .)