Agreed, war and death do not equal horror (in the literary sense at least). Horror is more of a pyschological attempt to scare you and make you question the deep dark places you don't like to think about. It taps into fears. Dark is just a description of the subject matter. It focuses on the same deep dark things and looks at the more nightmarish and/or deviant aspects of a situation (And I use deviant in the "seperate from the norm" way, not a kinky way). Men dying for their country isn't dark (Saving Private Ryan wasn't dark no matter how violent it was. It was horiffic, but it wasn't horror), but a man in a war who's gone a little crazy, and is taking pieces of his fallen friends to "keep them alive" is dark. (Maybe not the best example, but you can see what I mean) Also, don't confuse graphic violence with horror or dark. Violence without that psychological element or something to make it scary or meaningful is quite often just boring. There's nothing inherently interesting in someone chopping (or blowing) someone up. The reason WHY they do it is usually far more compelling.
