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Back on the main topic:

If you treat Ermor like a natural disaster that you have to kill you will probably make yourself lose. If you fight Ermor, and while you are doing that empire A kills empire B, then you will find yourself with a huge wasteland which doesn't much increase your strength, and empire A will then be twice as good as he was before. (Not to mention the risk that Ermor might kill you instead). Thus empire A is likely to win. Containment is a much better strategy against Ermor than direct assault. This is assuming MP, of course. In single player you have to kill Ermor immediately because the AI cannot handle Ermor.

Ermor isn't much good at clamhoarding, with no native water income and no ready supply of water mages. They've also got no blood income. Late in the game they have many weaknesses, not the least of which is their one-dimensional army and their poor quality SCs.