You forgot that there is always the option to peacefully coexist. I asked you for a Nap but you declined and attacked me.
In the other Invisible Swarm, the one hosted by Chris, Invisible Swarm 4, i tried Ermor SG for comparation purposes. Though my S.O.L. Ermor is more inflexible i like it more than the IS 4 Ermor. In IS 4 i am neighboring Turin (Tien Chi) and we peacefully coexisted until Turn 57. Now Turin got too mighty though and for the game's sake i have now canceled our Nap.
I like the undead themes not because they are powerful but because they are fun to play
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Ermor is a really good partner nation normally. They will happily give you their other gems for deathgems and sometimes even for gold. Also their god is normally flexible so they can probably forge you special stuff like uniques.
Ermors Dominion normally can be kept out too, so there is really no need to attack them.