While watching the first Godfather recently, I wondered why exactly, Michael needed to kill the heads of the five families and Moe Greene at the end, other than to "assume and consolidate his nepharious power". After all, he was moving the family to Vegas anyway. Here were my thoughts...

He had to get rid of Moe Greene to take over his hotel in Vegas, thats a given...He knew from his father that Barzini was gonna come after him, so he had to wipe out don Barzini before Barzini could do the same to Michael and take over his territory. Are my assumptions correct or am I way off?

Now, here's where its cloudy for me. Was the killing of Tattaglia, Stracci (sp?), and Cuneo just to prevent them from coming after the Corleones for killing Barzini, or was it something else???