A spot of open diplomacy appears to be in order as I desperately need help!
If anyone has met a certain Ermor undead menace I would very much like to hear from them
I will point out that while you may be pleased he is attacking me rather than you he will become absolutely huge if I go down as there are plenty of neutrals I am too weak to take around me (I don't even control all the provinces by my capital). So it won't just be my lands he adds and I have no other neighbours to gobble them up before he gets them. Ermor will have no trouble rolling over them if he can get past me.