When Barzini says the traffic in narcotics will be permitted but controlled,and Don Corleone will provide protection in the East,and so will be the peace, and Vito agrees to keep that peace, I think that they are strictly referring to ending the war over Narcotics. With 5 major Families all operating in New York, there have always been incursions into each others territory. Mostly,they are settled with sit downs, sometimes with more aggressive arbitration techniques. My point is that if Barzini was weaseling into the Corleone rackets,it was outside the scope of the peace agreement made at the Commission, since it didn't involve the drug business.