One of the theories is that Montagna aligned himself with Calabrian clans from Toronto which is quite interesting. Another theory is that New York was cleaning house in conjunction with the remnants of the old Cotroni faction, which seems more likely.
It's most likely a bit of both from what it seems. A collaboration between Toronto, NYC and old Cotroni members to get rid of the Rizzuto leadership.
The whole project seemed to be spearheaded by Montagna.
