Is it really that crazy? Casso did order the entire the death of the entire jersey faction which was a fight between a essentially a 200+ strong NY family was preparing to whack a large 50-60+, mostly independent jersey crew/family. The order was wipe out New Jersey. ... drew up a list of thirty Lucchese mobsters from the Garden State and dispatched assassins to kill them all.
The Jeresy family essentially told Casso/Amuso to eat it like Tony did in response to crazy demands for large kickups. Of course, rather than a war breaking out- guys started ratting.
In the case, all the Jersey guys went into hiding until the FBI started arresting everyone. The jersey guys never really fought back.