Sonny’s death made for a great scene, but what was the point behind it? Carlo was contacted by Barzini to sell Sonny out and set him up, but what is the meaning behind killing him? IMO, all things were settled between the Corleone’s and Tattaglia’s. They tried to kill Vito, and while it was unsure if Vito would make it, the Corleone’s took out Bruno. All things should have been settled between them.

So if Barzini was the only one behind the killing, why was he? What did he have to gain from it? Sonny was hot for the Sollozzo deal and by killing him, he dashed his hopes to get the Corleone’s aboard - even though they eventually did.