Oh, and where's the evidence that Michael was trying to muscle in on Roth's territory, or perhaps how Roth deduced he was going to.
Hi. Remember what Ola said..
"The casino you're interested in - the registered owners are Jacob Lawrence, Allan Barclay, both Beverly Hills attorneys. The real owners are the old Lakeville Road group from Cleveland, and our friend in Miami. Meyer Klingman runs the store; he owns a piece of it too; he does all right. But I've been instructed to tell you that if you move Klingman out, our friend in Miami will go along"....The Corleones hadn't been invited in; they were moving in. Michael was making Roth an offer Roth couldn't refuse. It was
"Hi. I'm your new partner now. We'll make more money that way. You don't, like, have a problem with that or anything, do you???"
Based on what had happened with Moe Greene when he had refused a similar request from the Corleones and Michael's interest in Cuban casinos , which evidently the Corleones hadn't previously had an interest in, Roth had every right to feel like he was under attack. He was. Sooner or later Michael would urge him/force him to retire permanently. That's why Roth was backing the Rosato brothers.