Showed that Vito Corleone was very wise to say 'No' to Sollozzo, then Sonny had to screw everything up.
I know. That was pretty much the crux of the whole story, wasn't it?
Not just in the movie, but in the history of organized crime in the United States, at least in the post-WWII time period.
It's like Mario Puzo basically nailed the pivot point of the whole story. The Godfather saw it coming. He was a genius, he saw it all. He just couldn't control things after he died, even though he tried to set things up so carefully.