Even though we all love the Corleones. We must give Barzini credit for his three involvment to injure the Corleone family.
1. Barzini used Paulie to hurt the Don because of his refusal to enter the narcotics business.
2. Barzini approaching Carlo Rizzi to kill Sonny (knowing he would help him since SOnny beat his ass!).
3. For making a deal with Tessio(AND I BELIEVE TESSIO BECAME A TRAITOR BECAUSE MICHAEL WOULD NOT LET CLEMENZA AND HIM BREAK OFF FROM THE FAMILY AND RUN THEIR OWN FAMILY THEY WAY THEY WANTED TOO.)
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I BELIEVE THAT IS WHY TESSIO BECAME A TRAITOR
BUT JUST FOR A COUNT...
WHO THINKS BARZINI PLANNED THIS ALL FROM THE VERY BEGINNING AND CARLO AND TESSIO WERE IN IT SINCE THE SHOOTING OF THE DON?????

"Well you just do what I tell you to do! Goddamn it! If I had a wartime consiglieri -- a
Sicilian -- I wouldn't be in this shape! Pop had Genco -- look what I got." - Sonny Corleone