Greg Cox wrote:
I suspect it was the Godfather movies that started the trend of numbering sequels, possibly because it seemed classier.
That was "Part II," though, not "II" - Possibly the earliest well-known plain IIs before TWoK
are Rocky II
and Superman II
(In some alternate universe this must have gone too far - e.g., Star Trek III: The Wrath of Khan II
directed by, of course, Christian I. Nyby II.)