The reason that I stated that THE GODFATHER II is more like a series component instead of a pure sequel is for this reason....

Often people critiicize sequels for being 'unnecessary' and MOST of them are. However, if a movie is done because it's part of a larger story already than it's not unnecessary, but rather made because one film was not enough to capture the entire over-arching story. Thus, LORD OF THE RINGS would have been silly if they only made the first part....it's only one installment of the entire saga.