score:5
The answer is absolutely zero. The Belgae people of 50 BC and the Belgians of today are in all likelihood completely genetically different - the area was resettled by Romans, as you say, but also suffered (and most likely bred with) various different Germans, Goths, Huns, Magyars and finally Vikings before we reach somewhere resembling today's modern Belgians.
If your question is "What have the people who have lived in the area conquered throughout history" then you could say the whole world (you did mention recursively) because the people in the region became French, Normans and Dutch, who then became other states like the UK, the USA, etc.
Although by the 1400's no French, Norman English or Flemish king has ever sat on the throne of: