It's been said, and I forget exactly where, that the Corleone Family was in a decline after the first Godfather movie. However, I don't see any evidence in the second movie that the Corleone Family had lost much of its power. I mean in the book, it says that the Corleone Family established itself as one of the most powerful Mafia families in the country after Michael defeated the Tattaglia and Barzini Families (in the book, he didn't execute the heads of the Five Families).
Of course, the book didn't go as far as the movies so it might not be fair to use it.
Now that I think about it. Perhaps moving out west reduced the power of the family since the big cities had the most influential Mafia families in the country. I don't know. What do you think?
This is a good topic. After the war with Barzini and the other families, the Corleones were dethroned as the most powerful New York outfit, and severely weakened. (The book says that Barzini had assumed the position the Corleones once had.) But this position of power was regained by the end of the book (and the movie). Michael, under Vito's instruction, made the Corleones look weaker than they actually were in order to prevent the other families from picking up on the scent of his extensive preparations for a brutal strike aimed not only at regaining but also expanding the Corleone's former supremacy in New York. (In the book Barzini and Greene are killed by Neri, and Tattaglia is killed by Rocco, if I'm not mistaken.)
When Michael refused to allow Tessio and Clemenza to take steps to curb the encroachments of Barzini's people on their territory, Tessio argued that Michael was wrong, and that the move to Nevada should be made from a position of strength in New York, not one of weakness. Tessio was right, but he didn't realize that Michael was well aware of this, which was why Michael was building a secret regime under Rocco Lampone. So again, when Michael makes the move to Nevada, he does so from a position of undisputed supremacy in New York. As the Chairman of the senate committee says, Michael had the heads of the Five Families killed "to
assume and
consolidate his nefarious power." On the other hand, there is the remark made by Tom that the Corleone Family "once was" like the Roman empire, which implies a decline of some kind. There is also the troubles caused by the Rosato's trying to break off from Clemenza and form their own completely independent family.
But by the beginning of GFIII Michael is exponentially more powerful than he ever was. Just think of his dismissive remarks about Joey Zasa, to the effect that he is a small time punk, and consider those remarks in light of Michael's comment to Vincent that Zasa is in charge of what used to be the Corelone family business in New York.
