I agree that war is horrible hence the term "Horror of war". Would you place "Saving Private Ryan" in the genre "Horror Movie" because it has nightmarish qualities?
Like Tony I have to have a startle, boo, unknown darkness quality to place it into that genre. As a matter of fact one of the worst scenes in Alien was where we saw it full body and all of a sudden it was a guy in a suit instead of this terrifying monster popping out of the darkness unseen.
So for me to declare something in the horror genre it requires the horror unseen. Alien had it, Aliens didn't. Even though you are correct that there was horror aplenty in both.
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