Also, calling what France did "assistance" is a euphemism and a half.
That's what it was, at first.
Then more aid, till finally took over the place slowly, Treaty Port by Treaty Port, Concession by Concession, mostly in the name of protecting Missionaries.
After 60 years controlled the South and Center, and 25 more, the North after a brief war with China over the North, while Cambodia and Laos a bit before that time.
But there was far more urge for Nationalism to unify in Germany and Italy, than had ever been in what we call Vietnam today.
Vietnam is much close to the UK, unified by force over generations, than a desire for unity. Over 50 ethnic groups, all with languages and customs far different from a Prussian to a Bavarian, or Lombard, Neapolitan or to a Sicilian in Italy