Since coming from Belgium Hercule finally with grounds for action (7)
I believe the answer is:
because
'since' is the definition.
(I've seen this before)
'belgium hercule finally with grounds for action' is the wordplay.
'belgium' becomes 'B' (international vehicle registration code).
'finally' suggests the final letters.
'with' means one lot of letters goes inside another.
'grounds for' becomes 'u' (I can't explain this - if you can you should believe this answer much more).
'action' becomes 'case' (synonyms).
The last letter of 'hercule' is 'e'.
'u' inserted within 'case' is 'cause'.
'b'+'e'+'cause'='BECAUSE'
'coming from' is the link.
Can you help me to learn more?
(Other definitions for because that I've seen before include "On account of" , "Owing to" , "Since" , "For the reason that" , "Thanks to this" .)