Well TB, not completely....Sonny is talking about killing EVERYONE not just Solozzo. Michael's conclusion that killing Vito is the key for Solozzo is based on evidence. He has seen that Solle Solozzo controlled the police who pulled the guards off of the Hospital watch so they could have another whack at Vito. This makes him realize that the "key" for Solozzo is killing Vito. It may well be the other families gave the go ahead to Sollozzo to do this, with the caveat that if he failed they would not back his drug business. OF course after Michael got slapped around, Sonny went off and killed Bruno Tattaglia ensuring there would be a full scale war...and he is bragging to Tom about having a hundred button men on the street.

I wonder... if Sonny had not killed Bruno, and if Michael had killed Sollozzo and McCluskey and fled to Sicily, couldn't a deal to avoid a full scale war been reached?