I have to disagree with Ironhawk (and only in part because I am playing Ermor in a game that he is in
) Of course this applies only to the undead themes of Ermor, which are most common.
Ermor's base troops are free, but this matters only if you attempt to fight them hand to hand with your base troops. Ermor, if he doesn't lose his troops in battles, may have several hundred or even thousand troops sitting around. However, most of these troops are completely useless. The weaker variants (Soulless for Ashen Empire, or Dispossessed Spirits for Soul Gate) are so bad in battle that about the only thing they can do is soak up hits. Longdeads for AE, or Spectral Legionnaires for SG, are slightly better. But they still have problems; longdeads never heal and have few HP, and SG's spectral soldiers have attacks that are negated by magic resistance. Pound for pound, these guys are really bad fighters.
It's true that Ermor gets stronger as the game goes on, but that is true of every empire. There's nothing special about Ermor. In fact, the longer the game goes on, the easier it gets to blow up huge numbers of undead troops.
Ermor's mages, while upkeep-free, are also tremendously expensive in initial cost. Its research is not really all that great, and its magical diversity (other than on the pretender) is practically nil.
Ermor's one big advantage is the number of points it has to spend on its pretender, which is far more than any other nation. Ermor's pretender will *always* be a competent SC, and will usually be more powerful than the pretenders of other empires, except those who focus on combat to the exclusion of all else.
Finally, Ermor has only one natural resource, magic gems. Most empires have gems, gold, and resources. They may tend to have more gems, but they have to spend this one resource on mages and many of their regular troops, that other nations could spend gold for. For instance, Ermor has to summon its archers, whereas other nations can buy them. Then they also have to spend their gems on summons and magic items like everyone else. Ermor has a horrible, chronic gem shortage.
Ironhawk's assessment of the Marignon dominion is wrong, but I have to take the blame, since I was the one that gave him the wrong information. Only the Marignon home province kills undead (and it continues to do so even if not controlled by Marignon). The rest of the Marignon dominion has only the usual enemy-dominion effects.