When Micheal kills everyone, and he announces it to Carlo, he obviously inclludes the names of the heads of all the families. I can understand why he would want to kill Barzini and Tatt but what did Cuneo and Stracci and the other heads of the families do other tham go along with the idea of selling drugs. Are we to infer they all gave Sol the green light to kill Vito or Barz the green light to kill Sonny? If they merely allied themselves with Barzini, they would have done so for business reaons only. Was this another case of overlikk by Mike, or was it his way of making a Statement that the Corleones were back, and that no one should dare trifle with them?