I think when Moe Green says "I talked to Barzini... I can make the deal and still keep my hotels" THAT lets Michael know that Moe is in bed with the Nemesis of his father.... leading to what Michael would have to eventually do... take care of the 5 families.
"What I want.... whats most important to me... is that I have a guarantee" - Train approaches.... Bang! Bang! Bang!
