The current theory is that Raynald Desjardins, Vittorio Mirarchi, Salvatore Montagna, Domenico Arcuri, and Joe Di Maulo formed all conspired as a somewhat democratic group to overthrew the Rizzutos. Nick Sr and Jr hadn't been spreading the wealth around, and the Arcuris had always been sorta marginalized. Montagna wanted to take over and stirred up as much sentiment as he could. Desjardins was close to Vito but ever since Francesco Arcadi ordered the death of one of his best friends, he held a grudge and really didn't give a shit. Montagna warns Nick to step down, Nick tells him to fuck off, and the killings happen.

Arcuri had always backed Montagna and Mirarchi and Di Maulo had always backed Desjardins. They started disagreeing over leadership of the entity that would usurp the Rizzutos. Sal shot first at one of Desjardin's guys. In the end most the soldiers on both sides got knocked down, a notable survivor being Tony Suzuki who worked for Montagna. In the end we all know what happened. Montagna was killed, but Raynald got life in prison.