Sonny, of course, tries to coordinate a massacre of the heads of all the other families, and there's various mentions of the Corleones fighting multiple families.

There is a very curious line in the Peace Conference scene, though: "What was more inportant was that Barzini by speaking out was saying that if peace was not made he would openly join the Tattaglias in their war against Corleones." Are we to think that, to that time, Barzini had appeared to be a bystander as Stracci and Cuneo were?