However, many of those Calabrians weren't really Calabrians. I've come to view the two historically rival factions as the "mainland Italian" faction (the Cotroni faction consisted predominantly of mainland Italians) vs. the Rizzuto (Sicilian) faction.

And I don't think vengeance played a big part in the attempted take-over. Di Maulo's loyalty mostly lay with his friend and mentor, Frank Cotroni, and I think it's reasonable to assume that Frank Cotroni and Paolo Violi weren't the best of friends, since his brother Vic chose Violi over Frank to become his second-in-command. As for Gallo, another major player of the old Cotroni group, he was ordered by Violi to commit a murder for which he needed to take the rap and do jail time. This very same murder would come to haunt Gallo many years later. When he was tried for violating his parole, Canadian authorities found out that he never obtained Canadian citizenship and started a deportation case against him, which he eventually lost. So I wonder why Gallo would've still felt any loyalty towards Violi.