After seeing parts of GFIII for the millionth time on cable (whydon't they show I & II this often?) it is abundantly clear how brilliantly Michael manipulated Vincent and Connie by naming Vincent to be the Godfather here is what he accomplished:

1. He got Vincent to break it off with Mary.

2. He got deniablity from Connie and Vincent about his giving up the life of a criminal to become legitimate.

3. He assuaged Connie's desire to see Vincent succeed.

4. He also fooled himself a bit by thinking that he would be redeemed if he becme a "hands off" mafioso.

Of course had Mary not been shot, Vincent would have run the day to day crime operations in New York, as he said had to be done in the meeting with Don Tomassino, and Michael would be the esteemed head of Immobiliare, while still controlling Vincent. Put differently, he turned Connie and Vincent into "buffas."

Michael tips his hand about legitimacy in the party meeting with Zasa and Vinnie when he asks Zasa what we do about a piece of s*** like that who says demeaning things about him. He still has that violent streak and he knows that violence is still part of his world. That's why he accepts Vinnie's offer to protect him.

As I've said before, it looked like Vincent was manipulating Michael. He crashed his party and buttered up his "favorite aunt" for an audience, with Connie reminding Michael, pointedly, that Vincent was "Sonny's boy." But could Vincent vanquish the all-time champion manipulator? Not a prayer! Vincent succeeded in rousing Michael from his Papal Knight reverie by reminding him that he has a powerful enemy. So Michael put him to the test: he called in Zasa and promptly humiliated Vincent ("that was foolish of you...Mr. Zasa gave you a job out of the goodness of his heart...make your peace with Mr. Joe Zasa..."). In effect, he threw Vincent to the dogs. He was testing Vincent--how much did Vincent want to be with him? He got his answer pronto when Vincent bit Zasa's ear, thus tying his very survival to Uncle Michael.

In the novel, Michael asks Vito why he needed Luca Brasi--"an animal like that?" Vito replies that "in this world there are men who run around shouting 'kill me, kill me.' " He says they can be very useful if you make yourself into the only one whom they fear and remain loyal. At that moment, Vincent became Michael's Luca.

Vincent later aquired a patina of civilization and thoughtfulness, as Olivant pointed out in another thread. All that did was expand the range of Michael's ability to manipulate Vincent, as detailed by dt in the original post here.