Let's be honest, Arcachon never had allies, Arcaea just had people who hated it in Zonasa.
Aenelia mostly helped out Arcachon to screw with Ohnar West are Arcaea risk-free, and got called on it. Arcachon spent years being total bastards to everyone and the whole shebang started on a C'thonia-like assault in Niel which was ne-ever going to succeed and has snowballed since then. Ciann and Terril have some personal allies, as do some of the others in the realm, but that's about it (aside from Ciann's spy network).
Boogie-man realms don't get to have allies. If Arcaea conquers Arcachon, they'll likely find themselves in the new role of boogie-man (though of a different kind), and will probably face similar isolation problems (unless Cathay goes full fascist). That's just how human minds work. There is a boogie-realm in every continent and there probably always will be. Though they manifest differently you can almost immediately point at them and go "Those guys!"
I'd really like to see Cathay take up the role of villian though (once Arcachon's gone, which, like all villians it one day will). It's harder for them to do though, but a fascist military state is a more interesting villian then a quasi-empire. Mostly because I'm not sure that a pure RP empire without mechanics to back it will survive the first fit of pique due to imperial succession and while empires make for interesting internal dynamic, they are often too nebulous to serve as the straight villian.
