>Well, the barbarian hordes overrunning us are coming from the south. Seems Rome had a problem controlling its borders and unwanted barbarian settlers, too.<
Actually, they weren't unwanted. They came to do the jobs average Romans didn't want to do.
Sadly, that really isn't a joke...
As to the question of intervention: I wouldn't be able to live with myself if I didn't. Die by a mob, or die by my own hand: at least option A means I stood for something.